<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:012accfc-77aa-4b04-935f-3b13a3f95234,g:f04dac30-b9ac-40be-9e6c-eba58878217b-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.pentair.com/role/ConsolidatedStatementsofChangesInEquity" xlink:type="simple" xlink:href="pnr-20251231.xsd#ConsolidatedStatementsofChangesInEquity"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/ConsolidatedStatementsofChangesInEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_41b3ccad-d72f-4c17-a046-be46f516d386" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_9e8da2d9-7962-4c58-b111-8fccfaffb645" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_41b3ccad-d72f-4c17-a046-be46f516d386" xlink:to="loc_us-gaap_StatementTable_9e8da2d9-7962-4c58-b111-8fccfaffb645" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_aa5c45fd-017f-4456-b9be-83c170b19578" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_9e8da2d9-7962-4c58-b111-8fccfaffb645" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_aa5c45fd-017f-4456-b9be-83c170b19578" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_aa5c45fd-017f-4456-b9be-83c170b19578_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_aa5c45fd-017f-4456-b9be-83c170b19578" xlink:to="loc_us-gaap_EquityComponentDomain_aa5c45fd-017f-4456-b9be-83c170b19578_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_b6e52c54-7938-4eea-aceb-9ed3dc57bdf5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_aa5c45fd-017f-4456-b9be-83c170b19578" xlink:to="loc_us-gaap_EquityComponentDomain_b6e52c54-7938-4eea-aceb-9ed3dc57bdf5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_2fd0b87d-2288-48f8-8a82-4a002dee7078" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b6e52c54-7938-4eea-aceb-9ed3dc57bdf5" xlink:to="loc_us-gaap_CommonStockMember_2fd0b87d-2288-48f8-8a82-4a002dee7078" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_ceff6f08-e0f9-4b92-89b1-25ed3ac18f35" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b6e52c54-7938-4eea-aceb-9ed3dc57bdf5" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_ceff6f08-e0f9-4b92-89b1-25ed3ac18f35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_fa6b4616-9c8b-40a6-bbd9-fcaf1e12ed95" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b6e52c54-7938-4eea-aceb-9ed3dc57bdf5" xlink:to="loc_us-gaap_RetainedEarningsMember_fa6b4616-9c8b-40a6-bbd9-fcaf1e12ed95" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_75c1ee40-ff12-48fd-9824-2e0f20dda0d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b6e52c54-7938-4eea-aceb-9ed3dc57bdf5" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_75c1ee40-ff12-48fd-9824-2e0f20dda0d6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramAxis_3cb577ce-b9f3-47f0-8d6a-39fe27fa3b71" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ShareRepurchaseProgramAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_9e8da2d9-7962-4c58-b111-8fccfaffb645" xlink:to="loc_srt_ShareRepurchaseProgramAxis_3cb577ce-b9f3-47f0-8d6a-39fe27fa3b71" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_3cb577ce-b9f3-47f0-8d6a-39fe27fa3b71_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ShareRepurchaseProgramAxis_3cb577ce-b9f3-47f0-8d6a-39fe27fa3b71" xlink:to="loc_srt_ShareRepurchaseProgramDomain_3cb577ce-b9f3-47f0-8d6a-39fe27fa3b71_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_3e31042a-25d1-4dac-9223-b2466ceefe19" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ShareRepurchaseProgramAxis_3cb577ce-b9f3-47f0-8d6a-39fe27fa3b71" xlink:to="loc_srt_ShareRepurchaseProgramDomain_3e31042a-25d1-4dac-9223-b2466ceefe19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_December2020ShareRepurchaseProgramMember_eef4e9c0-ee48-4432-8144-d8d8a6f57474" xlink:href="pnr-20251231.xsd#pnr_December2020ShareRepurchaseProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_3e31042a-25d1-4dac-9223-b2466ceefe19" xlink:to="loc_pnr_December2020ShareRepurchaseProgramMember_eef4e9c0-ee48-4432-8144-d8d8a6f57474" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_ce5884cf-4ede-4dd3-a084-c63be1d0fd2b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_41b3ccad-d72f-4c17-a046-be46f516d386" xlink:to="loc_us-gaap_SharesOutstanding_ce5884cf-4ede-4dd3-a084-c63be1d0fd2b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_1fafd919-bb72-4199-98b5-3d7df5959832" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_41b3ccad-d72f-4c17-a046-be46f516d386" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_1fafd919-bb72-4199-98b5-3d7df5959832" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_ed2e335e-6798-427b-95e0-da0662eccc1a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_41b3ccad-d72f-4c17-a046-be46f516d386" xlink:to="loc_us-gaap_ProfitLoss_ed2e335e-6798-427b-95e0-da0662eccc1a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_f17fdd66-db69-4076-bb26-331c9e22213a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_41b3ccad-d72f-4c17-a046-be46f516d386" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_f17fdd66-db69-4076-bb26-331c9e22213a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStock_9808d3e6-0dd0-487e-bbec-8a7e3a4f1560" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_41b3ccad-d72f-4c17-a046-be46f516d386" xlink:to="loc_us-gaap_DividendsCommonStock_9808d3e6-0dd0-487e-bbec-8a7e3a4f1560" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_fdaf2d9c-8340-4ea5-989e-e4e567be8fea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_41b3ccad-d72f-4c17-a046-be46f516d386" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_fdaf2d9c-8340-4ea5-989e-e4e567be8fea" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_012e5bf9-d287-42ec-9b40-f120d660ac19" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_41b3ccad-d72f-4c17-a046-be46f516d386" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_012e5bf9-d287-42ec-9b40-f120d660ac19" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_9eac0ca3-35f8-4d03-99e7-ed46800176c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_41b3ccad-d72f-4c17-a046-be46f516d386" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_9eac0ca3-35f8-4d03-99e7-ed46800176c9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_983d0422-6b77-4f60-ac6e-95608e8d4296" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_41b3ccad-d72f-4c17-a046-be46f516d386" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_983d0422-6b77-4f60-ac6e-95608e8d4296" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_a40b7cb0-a75e-4324-883d-729f14706e76" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_41b3ccad-d72f-4c17-a046-be46f516d386" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_a40b7cb0-a75e-4324-883d-729f14706e76" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_e105a45a-b092-48c8-b550-751dece48325" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_41b3ccad-d72f-4c17-a046-be46f516d386" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_e105a45a-b092-48c8-b550-751dece48325" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_SharesSurrenderedByEmployeesShares_a7354378-3ef1-4ac2-b49f-0b3e8ec9a1be" xlink:href="pnr-20251231.xsd#pnr_SharesSurrenderedByEmployeesShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_41b3ccad-d72f-4c17-a046-be46f516d386" xlink:to="loc_pnr_SharesSurrenderedByEmployeesShares_a7354378-3ef1-4ac2-b49f-0b3e8ec9a1be" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_SharesSurrenderedByEmployees_e10dfcde-c1a7-4333-8db4-a77a47f846ef" xlink:href="pnr-20251231.xsd#pnr_SharesSurrenderedByEmployees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_41b3ccad-d72f-4c17-a046-be46f516d386" xlink:to="loc_pnr_SharesSurrenderedByEmployees_e10dfcde-c1a7-4333-8db4-a77a47f846ef" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_abc6ce7f-9f46-419e-84e9-f7ab1efcf966" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_41b3ccad-d72f-4c17-a046-be46f516d386" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_abc6ce7f-9f46-419e-84e9-f7ab1efcf966" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_9cade84f-9707-4e31-9257-7802687c8a9e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_9bb42a8e-c29c-41eb-bdbd-0bb6efe6c9c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesBasisofPresentationDetails" xlink:type="simple" xlink:href="pnr-20251231.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesBasisofPresentationDetails"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesBasisofPresentationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_66ac36a6-2525-429c-9024-c30e1fc54365" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_523f6eb4-ee71-42c6-b504-8aa552d81f19" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_66ac36a6-2525-429c-9024-c30e1fc54365" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_523f6eb4-ee71-42c6-b504-8aa552d81f19" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_cb25511d-3451-44c7-b642-6a11ee7f18a9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_523f6eb4-ee71-42c6-b504-8aa552d81f19" xlink:to="loc_srt_RangeAxis_cb25511d-3451-44c7-b642-6a11ee7f18a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_cb25511d-3451-44c7-b642-6a11ee7f18a9_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_cb25511d-3451-44c7-b642-6a11ee7f18a9" xlink:to="loc_srt_RangeMember_cb25511d-3451-44c7-b642-6a11ee7f18a9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_d914a3aa-e493-4a81-8e1d-f736e6425900" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_cb25511d-3451-44c7-b642-6a11ee7f18a9" xlink:to="loc_srt_RangeMember_d914a3aa-e493-4a81-8e1d-f736e6425900" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_a10309da-e0c4-440a-87d8-d4acdaeea351" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_d914a3aa-e493-4a81-8e1d-f736e6425900" xlink:to="loc_srt_MinimumMember_a10309da-e0c4-440a-87d8-d4acdaeea351" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_16a183d9-34a4-424b-b2e2-a67fc6aa69b3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_d914a3aa-e493-4a81-8e1d-f736e6425900" xlink:to="loc_srt_MaximumMember_16a183d9-34a4-424b-b2e2-a67fc6aa69b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_ab3b3cf4-5997-4d16-b9ad-6feef4ab9c61" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_523f6eb4-ee71-42c6-b504-8aa552d81f19" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_ab3b3cf4-5997-4d16-b9ad-6feef4ab9c61" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_ab3b3cf4-5997-4d16-b9ad-6feef4ab9c61_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_ab3b3cf4-5997-4d16-b9ad-6feef4ab9c61" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_ab3b3cf4-5997-4d16-b9ad-6feef4ab9c61_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_c2f45f98-e3c0-42b9-b446-02be205e9d52" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_ab3b3cf4-5997-4d16-b9ad-6feef4ab9c61" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_c2f45f98-e3c0-42b9-b446-02be205e9d52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_InvesteesOtherMember_ff2754a2-f367-438a-89a8-b05749a65b21" xlink:href="pnr-20251231.xsd#pnr_InvesteesOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_c2f45f98-e3c0-42b9-b446-02be205e9d52" xlink:to="loc_pnr_InvesteesOtherMember_ff2754a2-f367-438a-89a8-b05749a65b21" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_5b9d9a18-8ad1-40c8-bc15-0c84c103d9c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_66ac36a6-2525-429c-9024-c30e1fc54365" xlink:to="loc_us-gaap_NumberOfReportableSegments_5b9d9a18-8ad1-40c8-bc15-0c84c103d9c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_d6c25f48-b47e-4efb-895c-ddc3aa126909" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_66ac36a6-2525-429c-9024-c30e1fc54365" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_d6c25f48-b47e-4efb-895c-ddc3aa126909" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesRevenueAdditionalInformationDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesRevenueAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesRevenueAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_348707df-8439-4023-b340-9a87ff5ee160" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_a742895b-ade7-4eb5-9a6d-353060ac0acc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_348707df-8439-4023-b340-9a87ff5ee160" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_a742895b-ade7-4eb5-9a6d-353060ac0acc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_09c5b543-ae12-42a2-996e-7e8684e793df" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TimingOfTransferOfGoodOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_a742895b-ade7-4eb5-9a6d-353060ac0acc" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_09c5b543-ae12-42a2-996e-7e8684e793df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_09c5b543-ae12-42a2-996e-7e8684e793df_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_09c5b543-ae12-42a2-996e-7e8684e793df" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_09c5b543-ae12-42a2-996e-7e8684e793df_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_61e2895a-0f89-4f1a-9d4f-1e78985b8314" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_09c5b543-ae12-42a2-996e-7e8684e793df" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_61e2895a-0f89-4f1a-9d4f-1e78985b8314" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferredAtPointInTimeMember_9f64c79c-4c7b-4814-93c4-b5ffbe24dcec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransferredAtPointInTimeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_61e2895a-0f89-4f1a-9d4f-1e78985b8314" xlink:to="loc_us-gaap_TransferredAtPointInTimeMember_9f64c79c-4c7b-4814-93c4-b5ffbe24dcec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferredOverTimeMember_abb5df55-c973-4af3-a372-a0bd3831459f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransferredOverTimeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_61e2895a-0f89-4f1a-9d4f-1e78985b8314" xlink:to="loc_us-gaap_TransferredOverTimeMember_abb5df55-c973-4af3-a372-a0bd3831459f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_2d8c4d36-0ffc-41f4-8fbc-4316153812ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_348707df-8439-4023-b340-9a87ff5ee160" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_2d8c4d36-0ffc-41f4-8fbc-4316153812ee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_RevenuesPercent_8a25da9d-9930-4b9c-8731-4fd72c940072" xlink:href="pnr-20251231.xsd#pnr_RevenuesPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_348707df-8439-4023-b340-9a87ff5ee160" xlink:to="loc_pnr_RevenuesPercent_8a25da9d-9930-4b9c-8731-4fd72c940072" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_7a4c5b56-7969-45dc-93ce-87d6305f3094" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_348707df-8439-4023-b340-9a87ff5ee160" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_7a4c5b56-7969-45dc-93ce-87d6305f3094" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_2f9a8cb7-d476-47b5-8134-d123833bb6e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_348707df-8439-4023-b340-9a87ff5ee160" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_2f9a8cb7-d476-47b5-8134-d123833bb6e1" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesPerformanceObligationsDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesPerformanceObligationsDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesPerformanceObligationsDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_a57fe227-ee79-4f7f-9909-5549fce30cab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_44fe9f1d-57d7-48fe-be69-1986c31864c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_a57fe227-ee79-4f7f-9909-5549fce30cab" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_44fe9f1d-57d7-48fe-be69-1986c31864c2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_ae1f6752-a46a-4041-b834-25e4691412c4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_44fe9f1d-57d7-48fe-be69-1986c31864c2" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_ae1f6752-a46a-4041-b834-25e4691412c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_23d707e5-39ff-406b-8c89-ff2327706874" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_44fe9f1d-57d7-48fe-be69-1986c31864c2" xlink:to="loc_srt_RangeAxis_23d707e5-39ff-406b-8c89-ff2327706874" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_23d707e5-39ff-406b-8c89-ff2327706874_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_23d707e5-39ff-406b-8c89-ff2327706874" xlink:to="loc_srt_RangeMember_23d707e5-39ff-406b-8c89-ff2327706874_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_3cd046e3-a17e-4716-ad59-2ec03929b3b3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_23d707e5-39ff-406b-8c89-ff2327706874" xlink:to="loc_srt_RangeMember_3cd046e3-a17e-4716-ad59-2ec03929b3b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_43f42056-da9f-4d7e-ab42-6f164c687dc0" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_3cd046e3-a17e-4716-ad59-2ec03929b3b3" xlink:to="loc_srt_MinimumMember_43f42056-da9f-4d7e-ab42-6f164c687dc0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_fa226413-665e-4ef1-a613-952e9f15095b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_3cd046e3-a17e-4716-ad59-2ec03929b3b3" xlink:to="loc_srt_MaximumMember_fa226413-665e-4ef1-a613-952e9f15095b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_a9e010ec-bba0-4f9a-8d87-14eb0000aeb1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_a57fe227-ee79-4f7f-9909-5549fce30cab" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_a9e010ec-bba0-4f9a-8d87-14eb0000aeb1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_06533ffc-3609-4417-8ce0-2cd0b7e40810" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_a57fe227-ee79-4f7f-9909-5549fce30cab" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_06533ffc-3609-4417-8ce0-2cd0b7e40810" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesPerformanceObligationsDetail_1" xlink:type="simple" xlink:href="pnr-20251231.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesPerformanceObligationsDetail_1"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesPerformanceObligationsDetail_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_a57fe227-ee79-4f7f-9909-5549fce30cab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_44fe9f1d-57d7-48fe-be69-1986c31864c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_a57fe227-ee79-4f7f-9909-5549fce30cab" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_44fe9f1d-57d7-48fe-be69-1986c31864c2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_23d707e5-39ff-406b-8c89-ff2327706874" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_44fe9f1d-57d7-48fe-be69-1986c31864c2" xlink:to="loc_srt_RangeAxis_23d707e5-39ff-406b-8c89-ff2327706874" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_23d707e5-39ff-406b-8c89-ff2327706874_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_23d707e5-39ff-406b-8c89-ff2327706874" xlink:to="loc_srt_RangeMember_23d707e5-39ff-406b-8c89-ff2327706874_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_3cd046e3-a17e-4716-ad59-2ec03929b3b3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_23d707e5-39ff-406b-8c89-ff2327706874" xlink:to="loc_srt_RangeMember_3cd046e3-a17e-4716-ad59-2ec03929b3b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_43f42056-da9f-4d7e-ab42-6f164c687dc0" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_3cd046e3-a17e-4716-ad59-2ec03929b3b3" xlink:to="loc_srt_MinimumMember_43f42056-da9f-4d7e-ab42-6f164c687dc0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_fa226413-665e-4ef1-a613-952e9f15095b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_3cd046e3-a17e-4716-ad59-2ec03929b3b3" xlink:to="loc_srt_MaximumMember_fa226413-665e-4ef1-a613-952e9f15095b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_a9e010ec-bba0-4f9a-8d87-14eb0000aeb1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_a57fe227-ee79-4f7f-9909-5549fce30cab" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_a9e010ec-bba0-4f9a-8d87-14eb0000aeb1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_06533ffc-3609-4417-8ce0-2cd0b7e40810" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_a57fe227-ee79-4f7f-9909-5549fce30cab" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_06533ffc-3609-4417-8ce0-2cd0b7e40810" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesNetSalesInformationDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesNetSalesInformationDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesNetSalesInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_9beea1c0-3941-48e2-aa74-c518d0a15caf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_146ae401-0024-4628-b1dc-01ac5606617b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_9beea1c0-3941-48e2-aa74-c518d0a15caf" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_146ae401-0024-4628-b1dc-01ac5606617b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_7f62fcc3-66d3-41d7-bfbc-13141ddad111" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_146ae401-0024-4628-b1dc-01ac5606617b" xlink:to="loc_srt_StatementGeographicalAxis_7f62fcc3-66d3-41d7-bfbc-13141ddad111" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_7f62fcc3-66d3-41d7-bfbc-13141ddad111_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_7f62fcc3-66d3-41d7-bfbc-13141ddad111" xlink:to="loc_srt_SegmentGeographicalDomain_7f62fcc3-66d3-41d7-bfbc-13141ddad111_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_af5dbded-858b-44a8-b07b-9d2973f6376d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_7f62fcc3-66d3-41d7-bfbc-13141ddad111" xlink:to="loc_srt_SegmentGeographicalDomain_af5dbded-858b-44a8-b07b-9d2973f6376d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_478aca31-c3d0-437c-867c-c3ce6dceb0ef" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_af5dbded-858b-44a8-b07b-9d2973f6376d" xlink:to="loc_country_US_478aca31-c3d0-437c-867c-c3ce6dceb0ef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_WesternEuropeMember_ee3d1cbd-9616-455e-a694-2bd6910e5e03" xlink:href="pnr-20251231.xsd#pnr_WesternEuropeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_af5dbded-858b-44a8-b07b-9d2973f6376d" xlink:to="loc_pnr_WesternEuropeMember_ee3d1cbd-9616-455e-a694-2bd6910e5e03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DevelopingCountriesMember_d1a8176e-3223-49e6-8726-dff2e113e9a5" xlink:href="pnr-20251231.xsd#pnr_DevelopingCountriesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_af5dbded-858b-44a8-b07b-9d2973f6376d" xlink:to="loc_pnr_DevelopingCountriesMember_d1a8176e-3223-49e6-8726-dff2e113e9a5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_OtherDevelopedCountriesMember_87aee327-8974-46fb-8cc6-28f7d834377a" xlink:href="pnr-20251231.xsd#pnr_OtherDevelopedCountriesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_af5dbded-858b-44a8-b07b-9d2973f6376d" xlink:to="loc_pnr_OtherDevelopedCountriesMember_87aee327-8974-46fb-8cc6-28f7d834377a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesByIndustryAxis_e4440e34-f901-490c-9fda-f3d4588aaab4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesByIndustryAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_146ae401-0024-4628-b1dc-01ac5606617b" xlink:to="loc_us-gaap_EquitySecuritiesByIndustryAxis_e4440e34-f901-490c-9fda-f3d4588aaab4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesIndustryMember_e4440e34-f901-490c-9fda-f3d4588aaab4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesIndustryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_EquitySecuritiesByIndustryAxis_e4440e34-f901-490c-9fda-f3d4588aaab4" xlink:to="loc_us-gaap_EquitySecuritiesIndustryMember_e4440e34-f901-490c-9fda-f3d4588aaab4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesIndustryMember_6397b3e1-84b3-49c4-ae0c-da13d0c209d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesIndustryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_EquitySecuritiesByIndustryAxis_e4440e34-f901-490c-9fda-f3d4588aaab4" xlink:to="loc_us-gaap_EquitySecuritiesIndustryMember_6397b3e1-84b3-49c4-ae0c-da13d0c209d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_ResidentialSectorMember_beda0a02-ca0c-45cf-8c1b-72f9dfdc8f9b" xlink:href="pnr-20251231.xsd#pnr_ResidentialSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_6397b3e1-84b3-49c4-ae0c-da13d0c209d6" xlink:to="loc_pnr_ResidentialSectorMember_beda0a02-ca0c-45cf-8c1b-72f9dfdc8f9b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_CommercialSectorMember_ce32d458-81ac-4195-882d-1de504b88537" xlink:href="pnr-20251231.xsd#pnr_CommercialSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_6397b3e1-84b3-49c4-ae0c-da13d0c209d6" xlink:to="loc_pnr_CommercialSectorMember_ce32d458-81ac-4195-882d-1de504b88537" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_IndustrialSectorMember_189ec201-3fca-46d5-9cbd-94f792a9e8fe" xlink:href="pnr-20251231.xsd#pnr_IndustrialSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_6397b3e1-84b3-49c4-ae0c-da13d0c209d6" xlink:to="loc_pnr_IndustrialSectorMember_189ec201-3fca-46d5-9cbd-94f792a9e8fe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_18e0374c-cf9f-4c2e-8e20-a80ad49856c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_9beea1c0-3941-48e2-aa74-c518d0a15caf" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_18e0374c-cf9f-4c2e-8e20-a80ad49856c2" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesEstimatedUsefulLivesofPropertyandEquipmentDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesEstimatedUsefulLivesofPropertyandEquipmentDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesEstimatedUsefulLivesofPropertyandEquipmentDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_aeb1faa4-95df-4cb2-be01-8fac5ba6a2d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_eea5d659-1929-4e00-b061-e868db519a56" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_aeb1faa4-95df-4cb2-be01-8fac5ba6a2d6" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_eea5d659-1929-4e00-b061-e868db519a56" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_bc071d8c-8097-4d63-b592-686c383a92c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_eea5d659-1929-4e00-b061-e868db519a56" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_bc071d8c-8097-4d63-b592-686c383a92c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_bc071d8c-8097-4d63-b592-686c383a92c0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_bc071d8c-8097-4d63-b592-686c383a92c0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_bc071d8c-8097-4d63-b592-686c383a92c0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_44d900a5-c8f7-4499-b918-a4886bdfe234" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_bc071d8c-8097-4d63-b592-686c383a92c0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_44d900a5-c8f7-4499-b918-a4886bdfe234" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandImprovementsMember_483a6bba-f237-49ad-a0ae-d8e448a6dc7a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LandImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_44d900a5-c8f7-4499-b918-a4886bdfe234" xlink:to="loc_us-gaap_LandImprovementsMember_483a6bba-f237-49ad-a0ae-d8e448a6dc7a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_BuildingsAndLeaseholdImprovementsMember_075dcba1-b255-4b54-aebf-4497f663cb1d" xlink:href="pnr-20251231.xsd#pnr_BuildingsAndLeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_44d900a5-c8f7-4499-b918-a4886bdfe234" xlink:to="loc_pnr_BuildingsAndLeaseholdImprovementsMember_075dcba1-b255-4b54-aebf-4497f663cb1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_583eb692-5dfc-4262-a846-98518f372834" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_44d900a5-c8f7-4499-b918-a4886bdfe234" xlink:to="loc_us-gaap_MachineryAndEquipmentMember_583eb692-5dfc-4262-a846-98518f372834" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_3a5d4453-2084-4de5-afb8-ee2ac4d5aa83" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_44d900a5-c8f7-4499-b918-a4886bdfe234" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_3a5d4453-2084-4de5-afb8-ee2ac4d5aa83" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_4810f313-7eba-4cd7-906f-6c44e1374b4a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_eea5d659-1929-4e00-b061-e868db519a56" xlink:to="loc_srt_RangeAxis_4810f313-7eba-4cd7-906f-6c44e1374b4a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_4810f313-7eba-4cd7-906f-6c44e1374b4a_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_4810f313-7eba-4cd7-906f-6c44e1374b4a" xlink:to="loc_srt_RangeMember_4810f313-7eba-4cd7-906f-6c44e1374b4a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_f6477e36-1501-4143-8857-90007506f559" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_4810f313-7eba-4cd7-906f-6c44e1374b4a" xlink:to="loc_srt_RangeMember_f6477e36-1501-4143-8857-90007506f559" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_a9134c4a-6eb7-4ca7-8134-68ed71e4b61e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_f6477e36-1501-4143-8857-90007506f559" xlink:to="loc_srt_MinimumMember_a9134c4a-6eb7-4ca7-8134-68ed71e4b61e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_2902c4f4-e399-4900-a8b3-db25ec8b2c14" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_f6477e36-1501-4143-8857-90007506f559" xlink:to="loc_srt_MaximumMember_2902c4f4-e399-4900-a8b3-db25ec8b2c14" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_3da40cf1-cbf8-4db7-a1da-ecde97ebf314" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_aeb1faa4-95df-4cb2-be01-8fac5ba6a2d6" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_3da40cf1-cbf8-4db7-a1da-ecde97ebf314" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesPropertyPlantandEquipmentbyGeographicLocationDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesPropertyPlantandEquipmentbyGeographicLocationDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesPropertyPlantandEquipmentbyGeographicLocationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_148c884e-506e-45ab-9921-8a8c8c8ea603" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_a2b8bd11-5343-42ea-9305-6bfb4e481b91" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_148c884e-506e-45ab-9921-8a8c8c8ea603" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_a2b8bd11-5343-42ea-9305-6bfb4e481b91" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_1d3385d1-9377-4007-937c-e4ace1e35077" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_a2b8bd11-5343-42ea-9305-6bfb4e481b91" xlink:to="loc_srt_StatementGeographicalAxis_1d3385d1-9377-4007-937c-e4ace1e35077" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_1d3385d1-9377-4007-937c-e4ace1e35077_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_1d3385d1-9377-4007-937c-e4ace1e35077" xlink:to="loc_srt_SegmentGeographicalDomain_1d3385d1-9377-4007-937c-e4ace1e35077_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_9137627a-f5e9-48e1-af31-65bca9c83e0c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_1d3385d1-9377-4007-937c-e4ace1e35077" xlink:to="loc_srt_SegmentGeographicalDomain_9137627a-f5e9-48e1-af31-65bca9c83e0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_7bc3dc59-a903-4f6b-a855-a3a00bb07ab8" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_9137627a-f5e9-48e1-af31-65bca9c83e0c" xlink:to="loc_country_US_7bc3dc59-a903-4f6b-a855-a3a00bb07ab8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_WesternEuropeMember_dd677e0b-1b2a-4bdd-b661-8af490f19dd0" xlink:href="pnr-20251231.xsd#pnr_WesternEuropeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_9137627a-f5e9-48e1-af31-65bca9c83e0c" xlink:to="loc_pnr_WesternEuropeMember_dd677e0b-1b2a-4bdd-b661-8af490f19dd0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DevelopingCountriesMember_bf5387d9-a9db-4a9f-abe2-80e6e2f1ece0" xlink:href="pnr-20251231.xsd#pnr_DevelopingCountriesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_9137627a-f5e9-48e1-af31-65bca9c83e0c" xlink:to="loc_pnr_DevelopingCountriesMember_bf5387d9-a9db-4a9f-abe2-80e6e2f1ece0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_OtherDevelopedCountriesMember_69147fab-fa42-4538-9440-2ad9f9a055df" xlink:href="pnr-20251231.xsd#pnr_OtherDevelopedCountriesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_9137627a-f5e9-48e1-af31-65bca9c83e0c" xlink:to="loc_pnr_OtherDevelopedCountriesMember_69147fab-fa42-4538-9440-2ad9f9a055df" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_c4c07c04-86e0-469b-a452-8b32826b3e02" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_148c884e-506e-45ab-9921-8a8c8c8ea603" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_c4c07c04-86e0-469b-a452-8b32826b3e02" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_f34cbb8b-d967-4250-95d4-d01bb1c98e3a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ImpairmentOfLongLivedAssetsHeldForUse"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_148c884e-506e-45ab-9921-8a8c8c8ea603" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_f34cbb8b-d967-4250-95d4-d01bb1c98e3a" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesInsuranceSubsidiaryDetails" xlink:type="simple" xlink:href="pnr-20251231.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesInsuranceSubsidiaryDetails"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesInsuranceSubsidiaryDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpenseLineItems_6900b608-d294-45fe-a7de-52f661602f41" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpenseLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpenseTable_db95f07b-ce56-403a-837a-1a92bb072e84" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpenseTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpenseLineItems_6900b608-d294-45fe-a7de-52f661602f41" xlink:to="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpenseTable_db95f07b-ce56-403a-837a-1a92bb072e84" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_00c3b600-aa66-406f-b642-5ad3c1740252" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpenseTable_db95f07b-ce56-403a-837a-1a92bb072e84" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_00c3b600-aa66-406f-b642-5ad3c1740252" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_00c3b600-aa66-406f-b642-5ad3c1740252_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_00c3b600-aa66-406f-b642-5ad3c1740252" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_00c3b600-aa66-406f-b642-5ad3c1740252_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_07626228-2033-486d-80d5-8eb38b589f23" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_00c3b600-aa66-406f-b642-5ad3c1740252" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_07626228-2033-486d-80d5-8eb38b589f23" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCurrentLiabilitiesMember_1b58b3a6-e046-482a-bc35-ff771c133a66" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCurrentLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_07626228-2033-486d-80d5-8eb38b589f23" xlink:to="loc_us-gaap_OtherCurrentLiabilitiesMember_1b58b3a6-e046-482a-bc35-ff771c133a66" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncurrentLiabilitiesMember_1d1fdbad-b0e1-4bb4-8420-6b025d357981" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNoncurrentLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_07626228-2033-486d-80d5-8eb38b589f23" xlink:to="loc_us-gaap_OtherNoncurrentLiabilitiesMember_1d1fdbad-b0e1-4bb4-8420-6b025d357981" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_2297e281-6311-4a73-8c38-8abea6a61d0e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpenseLineItems_6900b608-d294-45fe-a7de-52f661602f41" xlink:to="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_2297e281-6311-4a73-8c38-8abea6a61d0e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/AcquisitionsDetails" xlink:type="simple" xlink:href="pnr-20251231.xsd#AcquisitionsDetails"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/AcquisitionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_cea8205e-41e0-40e7-a56a-72873da63499" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_863e3431-6d05-49d1-85ff-90d7f3c7f5d0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_cea8205e-41e0-40e7-a56a-72873da63499" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_863e3431-6d05-49d1-85ff-90d7f3c7f5d0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_d503bbe2-1f25-4d5f-9a51-8cf6571a0cd4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_863e3431-6d05-49d1-85ff-90d7f3c7f5d0" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_d503bbe2-1f25-4d5f-9a51-8cf6571a0cd4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d503bbe2-1f25-4d5f-9a51-8cf6571a0cd4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_d503bbe2-1f25-4d5f-9a51-8cf6571a0cd4" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d503bbe2-1f25-4d5f-9a51-8cf6571a0cd4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_83aded36-68bd-43b5-82f3-a46a7f6e3cb8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_d503bbe2-1f25-4d5f-9a51-8cf6571a0cd4" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_83aded36-68bd-43b5-82f3-a46a7f6e3cb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_HydraStopLLCMember_ccad7f98-913d-4771-a683-546b34e51463" xlink:href="pnr-20251231.xsd#pnr_HydraStopLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_83aded36-68bd-43b5-82f3-a46a7f6e3cb8" xlink:to="loc_pnr_HydraStopLLCMember_ccad7f98-913d-4771-a683-546b34e51463" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_GFManufacturingLLCMember_72c80a02-aa44-42a0-baa6-d54a110ef3a8" xlink:href="pnr-20251231.xsd#pnr_GFManufacturingLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_83aded36-68bd-43b5-82f3-a46a7f6e3cb8" xlink:to="loc_pnr_GFManufacturingLLCMember_72c80a02-aa44-42a0-baa6-d54a110ef3a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_90f79fad-35d5-418e-a408-ac6802ecd831" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_863e3431-6d05-49d1-85ff-90d7f3c7f5d0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_90f79fad-35d5-418e-a408-ac6802ecd831" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_90f79fad-35d5-418e-a408-ac6802ecd831_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_90f79fad-35d5-418e-a408-ac6802ecd831" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_90f79fad-35d5-418e-a408-ac6802ecd831_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a53bea2f-bb37-40a8-ba5e-b26b2f02e1aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_90f79fad-35d5-418e-a408-ac6802ecd831" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a53bea2f-bb37-40a8-ba5e-b26b2f02e1aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_c78839f6-a63e-4458-a1f2-ac5aaf124950" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a53bea2f-bb37-40a8-ba5e-b26b2f02e1aa" xlink:to="loc_us-gaap_CustomerRelationshipsMember_c78839f6-a63e-4458-a1f2-ac5aaf124950" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_19e925b6-53c5-440d-b16d-e5d3fa807c68" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TechnologyBasedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a53bea2f-bb37-40a8-ba5e-b26b2f02e1aa" xlink:to="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_19e925b6-53c5-440d-b16d-e5d3fa807c68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_9233b9b1-c9de-48d2-b0e6-ab8678f1acf7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_cea8205e-41e0-40e7-a56a-72873da63499" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_9233b9b1-c9de-48d2-b0e6-ab8678f1acf7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_1e2e78e6-f082-429d-aeb2-bb5ee35d37e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_cea8205e-41e0-40e7-a56a-72873da63499" xlink:to="loc_us-gaap_Goodwill_1e2e78e6-f082-429d-aeb2-bb5ee35d37e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinitelivedIntangibleAssetsAcquired1_52acadeb-91ab-45a7-9f69-2e5becf9d31c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinitelivedIntangibleAssetsAcquired1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_cea8205e-41e0-40e7-a56a-72873da63499" xlink:to="loc_us-gaap_FinitelivedIntangibleAssetsAcquired1_52acadeb-91ab-45a7-9f69-2e5becf9d31c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_aca5fc9c-459f-4ec5-8e74-1514a1f40306" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_cea8205e-41e0-40e7-a56a-72873da63499" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_aca5fc9c-459f-4ec5-8e74-1514a1f40306" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_816cf0d1-e587-44c1-ab69-6c5c0d1ba7c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_cea8205e-41e0-40e7-a56a-72873da63499" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_816cf0d1-e587-44c1-ab69-6c5c0d1ba7c6" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/EarningsPerShareDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#EarningsPerShareDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/EarningsPerShareDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pnr_ComputationOfEarningsPerShareLineItems_30b2c0ba-8e7b-4016-beea-28e391ac061a" xlink:href="pnr-20251231.xsd#pnr_ComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_EarningsPerShareTable_84635c9b-02e5-4abd-85b3-723ad910b508" xlink:href="pnr-20251231.xsd#pnr_EarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pnr_ComputationOfEarningsPerShareLineItems_30b2c0ba-8e7b-4016-beea-28e391ac061a" xlink:to="loc_pnr_EarningsPerShareTable_84635c9b-02e5-4abd-85b3-723ad910b508" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_a5e28a64-8d35-4be2-88f2-da0f01cabbb3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pnr_EarningsPerShareTable_84635c9b-02e5-4abd-85b3-723ad910b508" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_a5e28a64-8d35-4be2-88f2-da0f01cabbb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_a5e28a64-8d35-4be2-88f2-da0f01cabbb3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_a5e28a64-8d35-4be2-88f2-da0f01cabbb3" xlink:to="loc_us-gaap_EquityComponentDomain_a5e28a64-8d35-4be2-88f2-da0f01cabbb3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_84b733ca-f44e-4071-8ae7-347577abb155" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_a5e28a64-8d35-4be2-88f2-da0f01cabbb3" xlink:to="loc_us-gaap_EquityComponentDomain_84b733ca-f44e-4071-8ae7-347577abb155" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_1b5fb37d-8b3d-4a0a-97b2-6ee8da08bbf4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_84b733ca-f44e-4071-8ae7-347577abb155" xlink:to="loc_us-gaap_RetainedEarningsMember_1b5fb37d-8b3d-4a0a-97b2-6ee8da08bbf4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_1122727c-0c6a-4478-a046-fa5515a34906" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_ComputationOfEarningsPerShareLineItems_30b2c0ba-8e7b-4016-beea-28e391ac061a" xlink:to="loc_us-gaap_NetIncomeLoss_1122727c-0c6a-4478-a046-fa5515a34906" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperations_3a17b4d7-77f5-45fc-8fa8-61bda5a45042" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_ComputationOfEarningsPerShareLineItems_30b2c0ba-8e7b-4016-beea-28e391ac061a" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperations_3a17b4d7-77f5-45fc-8fa8-61bda5a45042" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_99484965-646a-4acb-9519-116ab2fa55ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_ComputationOfEarningsPerShareLineItems_30b2c0ba-8e7b-4016-beea-28e391ac061a" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_99484965-646a-4acb-9519-116ab2fa55ca" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_f121729d-c4c2-4c44-9e2d-c4497e5ba9c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_99484965-646a-4acb-9519-116ab2fa55ca" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_f121729d-c4c2-4c44-9e2d-c4497e5ba9c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_90b668cb-f3ac-4583-b3de-eb0708afb607" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_99484965-646a-4acb-9519-116ab2fa55ca" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_90b668cb-f3ac-4583-b3de-eb0708afb607" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_a2833c10-8fb5-42b1-96d7-63c673f83ac4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_99484965-646a-4acb-9519-116ab2fa55ca" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_a2833c10-8fb5-42b1-96d7-63c673f83ac4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_EarningsPerShareNumeratorAbstract_677d956b-415e-47b8-b30a-c1071f01ed0a" xlink:href="pnr-20251231.xsd#pnr_EarningsPerShareNumeratorAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_ComputationOfEarningsPerShareLineItems_30b2c0ba-8e7b-4016-beea-28e391ac061a" xlink:to="loc_pnr_EarningsPerShareNumeratorAbstract_677d956b-415e-47b8-b30a-c1071f01ed0a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsPerBasicShare_80c8edbe-2412-46ca-9c9c-d7ee3f17b411" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsPerBasicShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_EarningsPerShareNumeratorAbstract_677d956b-415e-47b8-b30a-c1071f01ed0a" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsPerBasicShare_80c8edbe-2412-46ca-9c9c-d7ee3f17b411" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare_14256d14-3893-4345-8423-1238ef7e3ab3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_EarningsPerShareNumeratorAbstract_677d956b-415e-47b8-b30a-c1071f01ed0a" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare_14256d14-3893-4345-8423-1238ef7e3ab3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_c314e72b-67a3-406d-aeb3-2306ea08806b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_EarningsPerShareNumeratorAbstract_677d956b-415e-47b8-b30a-c1071f01ed0a" xlink:to="loc_us-gaap_EarningsPerShareBasic_c314e72b-67a3-406d-aeb3-2306ea08806b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare_4ff2a96c-1520-482b-9e3b-22f6deeabbb0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_EarningsPerShareNumeratorAbstract_677d956b-415e-47b8-b30a-c1071f01ed0a" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare_4ff2a96c-1520-482b-9e3b-22f6deeabbb0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare_95e8fa76-fb14-4529-85f2-590ac1b0121a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_EarningsPerShareNumeratorAbstract_677d956b-415e-47b8-b30a-c1071f01ed0a" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare_95e8fa76-fb14-4529-85f2-590ac1b0121a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_364f6f4e-b42c-487e-9a23-592cd8cea867" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_EarningsPerShareNumeratorAbstract_677d956b-415e-47b8-b30a-c1071f01ed0a" xlink:to="loc_us-gaap_EarningsPerShareDiluted_364f6f4e-b42c-487e-9a23-592cd8cea867" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_fda4ae73-5e5b-458f-805d-c14515f251fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_ComputationOfEarningsPerShareLineItems_30b2c0ba-8e7b-4016-beea-28e391ac061a" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_fda4ae73-5e5b-458f-805d-c14515f251fe" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/RestructuringandTransformationProgramCostsIncludedinSellingGeneralAdministrativeexpensesonConsolidatedStatementsofIncomeDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#RestructuringandTransformationProgramCostsIncludedinSellingGeneralAdministrativeexpensesonConsolidatedStatementsofIncomeDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/RestructuringandTransformationProgramCostsIncludedinSellingGeneralAdministrativeexpensesonConsolidatedStatementsofIncomeDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_9fb84d30-d7e5-432f-b2e5-923acb7a051a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_276d45ba-4cda-4f55-af11-1c6c5d4b1a11" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_9fb84d30-d7e5-432f-b2e5-923acb7a051a" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_276d45ba-4cda-4f55-af11-1c6c5d4b1a11" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_ce31ff88-f839-4915-9e05-9ffa10920ddd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_276d45ba-4cda-4f55-af11-1c6c5d4b1a11" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_ce31ff88-f839-4915-9e05-9ffa10920ddd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_ce31ff88-f839-4915-9e05-9ffa10920ddd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_ce31ff88-f839-4915-9e05-9ffa10920ddd" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_ce31ff88-f839-4915-9e05-9ffa10920ddd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_14ac27f7-74f0-49fb-afe9-477088a9bd86" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_ce31ff88-f839-4915-9e05-9ffa10920ddd" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_14ac27f7-74f0-49fb-afe9-477088a9bd86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_SeveranceAndRelatedCostsMember_956a8ace-fcd8-4c10-a3ba-3ac6a477d87b" xlink:href="pnr-20251231.xsd#pnr_SeveranceAndRelatedCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_14ac27f7-74f0-49fb-afe9-477088a9bd86" xlink:to="loc_pnr_SeveranceAndRelatedCostsMember_956a8ace-fcd8-4c10-a3ba-3ac6a477d87b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_AssetImpairmentAndWriteOffsMember_7e0a733d-869e-4f13-9a17-ee415252d1cb" xlink:href="pnr-20251231.xsd#pnr_AssetImpairmentAndWriteOffsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_14ac27f7-74f0-49fb-afe9-477088a9bd86" xlink:to="loc_pnr_AssetImpairmentAndWriteOffsMember_7e0a733d-869e-4f13-9a17-ee415252d1cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherRestructuringMember_e22a6271-6242-4cbc-b549-6e325e54dd1e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherRestructuringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_14ac27f7-74f0-49fb-afe9-477088a9bd86" xlink:to="loc_us-gaap_OtherRestructuringMember_e22a6271-6242-4cbc-b549-6e325e54dd1e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TransformationTypeAxis_d820f297-a058-47a5-a32f-a563d407bea5" xlink:href="pnr-20251231.xsd#pnr_TransformationTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_276d45ba-4cda-4f55-af11-1c6c5d4b1a11" xlink:to="loc_pnr_TransformationTypeAxis_d820f297-a058-47a5-a32f-a563d407bea5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TransformationTypeDomain_d820f297-a058-47a5-a32f-a563d407bea5_default" xlink:href="pnr-20251231.xsd#pnr_TransformationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_pnr_TransformationTypeAxis_d820f297-a058-47a5-a32f-a563d407bea5" xlink:to="loc_pnr_TransformationTypeDomain_d820f297-a058-47a5-a32f-a563d407bea5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TransformationTypeDomain_bd2a55e1-8599-46e6-a097-786a52217174" xlink:href="pnr-20251231.xsd#pnr_TransformationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_pnr_TransformationTypeAxis_d820f297-a058-47a5-a32f-a563d407bea5" xlink:to="loc_pnr_TransformationTypeDomain_bd2a55e1-8599-46e6-a097-786a52217174" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_SeveranceAndRelatedCostsMember_fb616a92-f57b-4549-94a7-09e69080a136" xlink:href="pnr-20251231.xsd#pnr_SeveranceAndRelatedCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_TransformationTypeDomain_bd2a55e1-8599-46e6-a097-786a52217174" xlink:to="loc_pnr_SeveranceAndRelatedCostsMember_fb616a92-f57b-4549-94a7-09e69080a136" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_AssetImpairmentsAndWriteOffsMember_4dbd25fb-6cb6-4f24-9899-4273d56067be" xlink:href="pnr-20251231.xsd#pnr_AssetImpairmentsAndWriteOffsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_TransformationTypeDomain_bd2a55e1-8599-46e6-a097-786a52217174" xlink:to="loc_pnr_AssetImpairmentsAndWriteOffsMember_4dbd25fb-6cb6-4f24-9899-4273d56067be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_OtherTransformationMember_151e87bd-e2bd-47be-b4db-fb067a8464d0" xlink:href="pnr-20251231.xsd#pnr_OtherTransformationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_TransformationTypeDomain_bd2a55e1-8599-46e6-a097-786a52217174" xlink:to="loc_pnr_OtherTransformationMember_151e87bd-e2bd-47be-b4db-fb067a8464d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_631d73a6-a71d-4387-b61e-33a56e82f65a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_9fb84d30-d7e5-432f-b2e5-923acb7a051a" xlink:to="loc_us-gaap_RestructuringCharges_631d73a6-a71d-4387-b61e-33a56e82f65a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TransformationCosts_69099f89-4efa-43c6-b62a-1127905d01f1" xlink:href="pnr-20251231.xsd#pnr_TransformationCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_9fb84d30-d7e5-432f-b2e5-923acb7a051a" xlink:to="loc_pnr_TransformationCosts_69099f89-4efa-43c6-b62a-1127905d01f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TotalRestructuringAndTransformationCosts_9e8443da-9e8b-4c44-8406-77a37da739a3" xlink:href="pnr-20251231.xsd#pnr_TotalRestructuringAndTransformationCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_9fb84d30-d7e5-432f-b2e5-923acb7a051a" xlink:to="loc_pnr_TotalRestructuringAndTransformationCosts_9e8443da-9e8b-4c44-8406-77a37da739a3" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/RestructuringandTransformationProgramRestructuringCostsbySegmentDetails" xlink:type="simple" xlink:href="pnr-20251231.xsd#RestructuringandTransformationProgramRestructuringCostsbySegmentDetails"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/RestructuringandTransformationProgramRestructuringCostsbySegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_9c91ced1-2290-4269-ac63-a1c0a9104b3b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_a117086b-cb52-44b1-be6e-407e4be9ff29" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_9c91ced1-2290-4269-ac63-a1c0a9104b3b" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_a117086b-cb52-44b1-be6e-407e4be9ff29" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_b4e15571-8cd6-4a04-895a-0b28ed5b5dcf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_a117086b-cb52-44b1-be6e-407e4be9ff29" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_b4e15571-8cd6-4a04-895a-0b28ed5b5dcf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_b4e15571-8cd6-4a04-895a-0b28ed5b5dcf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_b4e15571-8cd6-4a04-895a-0b28ed5b5dcf" xlink:to="loc_us-gaap_SegmentDomain_b4e15571-8cd6-4a04-895a-0b28ed5b5dcf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_6ddf7854-a0ff-4360-b8d6-5b3a79837387" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_b4e15571-8cd6-4a04-895a-0b28ed5b5dcf" xlink:to="loc_us-gaap_SegmentDomain_6ddf7854-a0ff-4360-b8d6-5b3a79837387" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_FlowMember_40929337-87cd-49ab-a9e3-9a4f496ff53f" xlink:href="pnr-20251231.xsd#pnr_FlowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_6ddf7854-a0ff-4360-b8d6-5b3a79837387" xlink:to="loc_pnr_FlowMember_40929337-87cd-49ab-a9e3-9a4f496ff53f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_WaterSolutionsMember_bff3563d-fe50-4dbf-80de-fcdb49e66ad1" xlink:href="pnr-20251231.xsd#pnr_WaterSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_6ddf7854-a0ff-4360-b8d6-5b3a79837387" xlink:to="loc_pnr_WaterSolutionsMember_bff3563d-fe50-4dbf-80de-fcdb49e66ad1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_PoolMember_a0ba0b47-d04c-4a44-82bf-e5b07ea9beb0" xlink:href="pnr-20251231.xsd#pnr_PoolMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_6ddf7854-a0ff-4360-b8d6-5b3a79837387" xlink:to="loc_pnr_PoolMember_a0ba0b47-d04c-4a44-82bf-e5b07ea9beb0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_15dd0bc3-42e4-46a9-86e0-71f735450d7f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_a117086b-cb52-44b1-be6e-407e4be9ff29" xlink:to="loc_srt_ConsolidationItemsAxis_15dd0bc3-42e4-46a9-86e0-71f735450d7f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_15dd0bc3-42e4-46a9-86e0-71f735450d7f_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_15dd0bc3-42e4-46a9-86e0-71f735450d7f" xlink:to="loc_srt_ConsolidationItemsDomain_15dd0bc3-42e4-46a9-86e0-71f735450d7f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_c4bf154d-a09b-4cd1-bb3e-4e4d1ba0231e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_15dd0bc3-42e4-46a9-86e0-71f735450d7f" xlink:to="loc_srt_ConsolidationItemsDomain_c4bf154d-a09b-4cd1-bb3e-4e4d1ba0231e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_7ac34bce-3d8d-4b20-b580-6f44591142c8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_c4bf154d-a09b-4cd1-bb3e-4e4d1ba0231e" xlink:to="loc_us-gaap_OperatingSegmentsMember_7ac34bce-3d8d-4b20-b580-6f44591142c8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_a785c38d-efdc-4f91-9c86-94a466f43e46" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_c4bf154d-a09b-4cd1-bb3e-4e4d1ba0231e" xlink:to="loc_us-gaap_CorporateNonSegmentMember_a785c38d-efdc-4f91-9c86-94a466f43e46" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TotalRestructuringAndTransformationCosts_2d262446-5ec8-40a8-a172-eff9e9d34d7c" xlink:href="pnr-20251231.xsd#pnr_TotalRestructuringAndTransformationCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_9c91ced1-2290-4269-ac63-a1c0a9104b3b" xlink:to="loc_pnr_TotalRestructuringAndTransformationCosts_2d262446-5ec8-40a8-a172-eff9e9d34d7c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/GoodwillandOtherIdentifiableIntangibleAssetsChangesinCarryingAmountofGoodwillbySegmentDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#GoodwillandOtherIdentifiableIntangibleAssetsChangesinCarryingAmountofGoodwillbySegmentDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/GoodwillandOtherIdentifiableIntangibleAssetsChangesinCarryingAmountofGoodwillbySegmentDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_6f0a0859-6ae7-42f6-a434-06d8c8369c77" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_ff42d722-6346-4579-92d8-b977dfbb05ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_6f0a0859-6ae7-42f6-a434-06d8c8369c77" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_ff42d722-6346-4579-92d8-b977dfbb05ff" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_00951392-f0a9-4f9e-adf0-6f77e28d5817" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_ff42d722-6346-4579-92d8-b977dfbb05ff" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_00951392-f0a9-4f9e-adf0-6f77e28d5817" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_00951392-f0a9-4f9e-adf0-6f77e28d5817_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_00951392-f0a9-4f9e-adf0-6f77e28d5817" xlink:to="loc_us-gaap_SegmentDomain_00951392-f0a9-4f9e-adf0-6f77e28d5817_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_9d6be36f-4d61-4af0-93e7-f080c3e9dad8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_00951392-f0a9-4f9e-adf0-6f77e28d5817" xlink:to="loc_us-gaap_SegmentDomain_9d6be36f-4d61-4af0-93e7-f080c3e9dad8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_FlowMember_7895f0a7-438b-4da0-9e89-371c65678981" xlink:href="pnr-20251231.xsd#pnr_FlowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_9d6be36f-4d61-4af0-93e7-f080c3e9dad8" xlink:to="loc_pnr_FlowMember_7895f0a7-438b-4da0-9e89-371c65678981" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_WaterSolutionsMember_4004799f-9fc1-4f49-a56e-2ebb540489f5" xlink:href="pnr-20251231.xsd#pnr_WaterSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_9d6be36f-4d61-4af0-93e7-f080c3e9dad8" xlink:to="loc_pnr_WaterSolutionsMember_4004799f-9fc1-4f49-a56e-2ebb540489f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_PoolMember_f263d851-3c35-4ead-bdc7-c4a0f43193c5" xlink:href="pnr-20251231.xsd#pnr_PoolMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_9d6be36f-4d61-4af0-93e7-f080c3e9dad8" xlink:to="loc_pnr_PoolMember_f263d851-3c35-4ead-bdc7-c4a0f43193c5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillRollForward_4569e2fd-8aed-43c2-b68a-81359e93ba58" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_6f0a0859-6ae7-42f6-a434-06d8c8369c77" xlink:to="loc_us-gaap_GoodwillRollForward_4569e2fd-8aed-43c2-b68a-81359e93ba58" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_13512dba-ab8b-4243-a6f0-f910ca44584a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_4569e2fd-8aed-43c2-b68a-81359e93ba58" xlink:to="loc_us-gaap_Goodwill_13512dba-ab8b-4243-a6f0-f910ca44584a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillAcquiredDuringPeriod_d2c9af78-d3a4-4699-a88f-b785a0395e13" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillAcquiredDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_4569e2fd-8aed-43c2-b68a-81359e93ba58" xlink:to="loc_us-gaap_GoodwillAcquiredDuringPeriod_d2c9af78-d3a4-4699-a88f-b785a0395e13" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillOtherIncreaseDecrease_2ff4cf8a-ae16-46c6-b7df-e18214adc2f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillOtherIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_4569e2fd-8aed-43c2-b68a-81359e93ba58" xlink:to="loc_us-gaap_GoodwillOtherIncreaseDecrease_2ff4cf8a-ae16-46c6-b7df-e18214adc2f1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_2f2b2d09-3998-419f-9d6e-f71b3bfe1c72" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/GoodwillandOtherIdentifiableIntangibleAssetsIdentifiableIntangibleAssetsDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#GoodwillandOtherIdentifiableIntangibleAssetsIdentifiableIntangibleAssetsDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/GoodwillandOtherIdentifiableIntangibleAssetsIdentifiableIntangibleAssetsDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pnr_AcquiredIntangibleAssetsByMajorClassLineItems_bf8b48c8-6fc2-4992-a1f7-7531818c0543" xlink:href="pnr-20251231.xsd#pnr_AcquiredIntangibleAssetsByMajorClassLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_ScheduleOfAcquiredIntangibleAssetsByMajorClassTable_a3fbeee0-3603-4a57-995c-75d1f5e07a47" xlink:href="pnr-20251231.xsd#pnr_ScheduleOfAcquiredIntangibleAssetsByMajorClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pnr_AcquiredIntangibleAssetsByMajorClassLineItems_bf8b48c8-6fc2-4992-a1f7-7531818c0543" xlink:to="loc_pnr_ScheduleOfAcquiredIntangibleAssetsByMajorClassTable_a3fbeee0-3603-4a57-995c-75d1f5e07a47" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_36511fef-2bf1-4e8a-b723-a6e060505d12" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pnr_ScheduleOfAcquiredIntangibleAssetsByMajorClassTable_a3fbeee0-3603-4a57-995c-75d1f5e07a47" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_36511fef-2bf1-4e8a-b723-a6e060505d12" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_36511fef-2bf1-4e8a-b723-a6e060505d12_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_36511fef-2bf1-4e8a-b723-a6e060505d12" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_36511fef-2bf1-4e8a-b723-a6e060505d12_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3c9994fa-9cbf-430f-b891-e16c709682d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_36511fef-2bf1-4e8a-b723-a6e060505d12" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3c9994fa-9cbf-430f-b891-e16c709682d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_d46cbbfb-3ef8-426a-9660-90d8f343af56" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3c9994fa-9cbf-430f-b891-e16c709682d2" xlink:to="loc_us-gaap_CustomerRelationshipsMember_d46cbbfb-3ef8-426a-9660-90d8f343af56" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PatentedTechnologyMember_8226e25f-aa66-4f97-9ba0-542808db6b1c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PatentedTechnologyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3c9994fa-9cbf-430f-b891-e16c709682d2" xlink:to="loc_us-gaap_PatentedTechnologyMember_8226e25f-aa66-4f97-9ba0-542808db6b1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_52a95c47-f883-4d64-aac6-b95446eb47f4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_AcquiredIntangibleAssetsByMajorClassLineItems_bf8b48c8-6fc2-4992-a1f7-7531818c0543" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_52a95c47-f883-4d64-aac6-b95446eb47f4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_ae4a8cfa-404d-4070-9712-14febb0e3ba7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_AcquiredIntangibleAssetsByMajorClassLineItems_bf8b48c8-6fc2-4992-a1f7-7531818c0543" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_ae4a8cfa-404d-4070-9712-14febb0e3ba7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_c0828117-f6d1-4ec8-bd75-a7a8842265be" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_AcquiredIntangibleAssetsByMajorClassLineItems_bf8b48c8-6fc2-4992-a1f7-7531818c0543" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_c0828117-f6d1-4ec8-bd75-a7a8842265be" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_44dea6bf-5592-4c9d-aca1-20b02df9923a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_AcquiredIntangibleAssetsByMajorClassLineItems_bf8b48c8-6fc2-4992-a1f7-7531818c0543" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_44dea6bf-5592-4c9d-aca1-20b02df9923a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_83ce1ec2-bb7f-4e60-bd54-db28a8d5e176" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_AcquiredIntangibleAssetsByMajorClassLineItems_bf8b48c8-6fc2-4992-a1f7-7531818c0543" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_83ce1ec2-bb7f-4e60-bd54-db28a8d5e176" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_4cbe5157-851a-4a34-bb67-bbef8067643a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_AcquiredIntangibleAssetsByMajorClassLineItems_bf8b48c8-6fc2-4992-a1f7-7531818c0543" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_4cbe5157-851a-4a34-bb67-bbef8067643a" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/DebtDebtOutstandingandAverageInterestRatesDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#DebtDebtOutstandingandAverageInterestRatesDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/DebtDebtOutstandingandAverageInterestRatesDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_874a7515-f3da-47fb-a8d0-ad543680631e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_0c215963-85ce-4c10-938b-c9c4d002c94a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_874a7515-f3da-47fb-a8d0-ad543680631e" xlink:to="loc_us-gaap_DebtInstrumentTable_0c215963-85ce-4c10-938b-c9c4d002c94a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_9dbdea60-c397-4216-9c78-b14554530cd7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_0c215963-85ce-4c10-938b-c9c4d002c94a" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_9dbdea60-c397-4216-9c78-b14554530cd7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_9dbdea60-c397-4216-9c78-b14554530cd7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_9dbdea60-c397-4216-9c78-b14554530cd7" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_9dbdea60-c397-4216-9c78-b14554530cd7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_e040991a-4cc5-49ff-a079-5f6dbcbb10cb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_9dbdea60-c397-4216-9c78-b14554530cd7" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_e040991a-4cc5-49ff-a079-5f6dbcbb10cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_5fffea0f-2531-4401-ad2e-1c3a7ef6cf81" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e040991a-4cc5-49ff-a079-5f6dbcbb10cb" xlink:to="loc_us-gaap_LineOfCreditMember_5fffea0f-2531-4401-ad2e-1c3a7ef6cf81" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TermLoansMember_71b3b21a-a55a-44bd-8a12-f620d4a4f695" xlink:href="pnr-20251231.xsd#pnr_TermLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e040991a-4cc5-49ff-a079-5f6dbcbb10cb" xlink:to="loc_pnr_TermLoansMember_71b3b21a-a55a-44bd-8a12-f620d4a4f695" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_da538354-3b7a-45f0-bda1-a9e4d5e37497" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e040991a-4cc5-49ff-a079-5f6dbcbb10cb" xlink:to="loc_us-gaap_SeniorNotesMember_da538354-3b7a-45f0-bda1-a9e4d5e37497" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_873270a5-8179-4ff2-9650-0cbbcc405ac9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_0c215963-85ce-4c10-938b-c9c4d002c94a" xlink:to="loc_us-gaap_DebtInstrumentAxis_873270a5-8179-4ff2-9650-0cbbcc405ac9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_873270a5-8179-4ff2-9650-0cbbcc405ac9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_873270a5-8179-4ff2-9650-0cbbcc405ac9" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_873270a5-8179-4ff2-9650-0cbbcc405ac9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_8d8d37b3-cbc1-4da8-9eb7-d6fe98fbe31a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_873270a5-8179-4ff2-9650-0cbbcc405ac9" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_8d8d37b3-cbc1-4da8-9eb7-d6fe98fbe31a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_A5YearTermLoanFacilityMember_5bbc62dd-c17e-47d1-8e00-9fcf5f4065bd" xlink:href="pnr-20251231.xsd#pnr_A5YearTermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_8d8d37b3-cbc1-4da8-9eb7-d6fe98fbe31a" xlink:to="loc_pnr_A5YearTermLoanFacilityMember_5bbc62dd-c17e-47d1-8e00-9fcf5f4065bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_SeniorNotesFourPointSixFivePercentDueTwentyTwentyFiveMember_fa9aaa2e-04c7-4889-9528-d4b01dea5563" xlink:href="pnr-20251231.xsd#pnr_SeniorNotesFourPointSixFivePercentDueTwentyTwentyFiveMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_8d8d37b3-cbc1-4da8-9eb7-d6fe98fbe31a" xlink:to="loc_pnr_SeniorNotesFourPointSixFivePercentDueTwentyTwentyFiveMember_fa9aaa2e-04c7-4889-9528-d4b01dea5563" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_SeniorNotes4.500duein2029Member_9a61c70e-e6c0-4629-ba0a-8e9a287a49fa" xlink:href="pnr-20251231.xsd#pnr_SeniorNotes4.500duein2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_8d8d37b3-cbc1-4da8-9eb7-d6fe98fbe31a" xlink:to="loc_pnr_SeniorNotes4.500duein2029Member_9a61c70e-e6c0-4629-ba0a-8e9a287a49fa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_SeniorNotesFivePointNinePercentDueTwentyThirtyTwoMember_1f34fbff-ca47-4393-bce8-015df44f10e5" xlink:href="pnr-20251231.xsd#pnr_SeniorNotesFivePointNinePercentDueTwentyThirtyTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_8d8d37b3-cbc1-4da8-9eb7-d6fe98fbe31a" xlink:to="loc_pnr_SeniorNotesFivePointNinePercentDueTwentyThirtyTwoMember_1f34fbff-ca47-4393-bce8-015df44f10e5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_4c12d041-bf3e-465f-9b10-4702a7401a5d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_0c215963-85ce-4c10-938b-c9c4d002c94a" xlink:to="loc_us-gaap_CreditFacilityAxis_4c12d041-bf3e-465f-9b10-4702a7401a5d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_4c12d041-bf3e-465f-9b10-4702a7401a5d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_4c12d041-bf3e-465f-9b10-4702a7401a5d" xlink:to="loc_us-gaap_CreditFacilityDomain_4c12d041-bf3e-465f-9b10-4702a7401a5d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_298f0ce4-01b1-4da6-a9af-c6f5532981bf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_4c12d041-bf3e-465f-9b10-4702a7401a5d" xlink:to="loc_us-gaap_CreditFacilityDomain_298f0ce4-01b1-4da6-a9af-c6f5532981bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_1f507405-2b52-43d4-9cb6-ccb0135e9d88" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_298f0ce4-01b1-4da6-a9af-c6f5532981bf" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_1f507405-2b52-43d4-9cb6-ccb0135e9d88" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtWeightedAverageInterestRate_8bd464a2-b655-423a-8bd1-ae8f149424fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtWeightedAverageInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_874a7515-f3da-47fb-a8d0-ad543680631e" xlink:to="loc_us-gaap_DebtWeightedAverageInterestRate_8bd464a2-b655-423a-8bd1-ae8f149424fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_fa10efd1-af74-4784-8886-7f9b9a119c18" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_874a7515-f3da-47fb-a8d0-ad543680631e" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_fa10efd1-af74-4784-8886-7f9b9a119c18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherShortTermBorrowings_9ddfd487-e8ff-40d3-9437-f7046ec31a48" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherShortTermBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_874a7515-f3da-47fb-a8d0-ad543680631e" xlink:to="loc_us-gaap_OtherShortTermBorrowings_9ddfd487-e8ff-40d3-9437-f7046ec31a48" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_b2033c78-6352-4df9-8154-a8d3ded5fd55" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_874a7515-f3da-47fb-a8d0-ad543680631e" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_b2033c78-6352-4df9-8154-a8d3ded5fd55" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_02fe45a5-6cc7-473b-90d0-8664d2ef0451" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtLongtermAndShorttermCombinedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_874a7515-f3da-47fb-a8d0-ad543680631e" xlink:to="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_02fe45a5-6cc7-473b-90d0-8664d2ef0451" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_39d19f8d-10cf-4060-aa77-46407489c74c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_874a7515-f3da-47fb-a8d0-ad543680631e" xlink:to="loc_us-gaap_LongTermDebt_39d19f8d-10cf-4060-aa77-46407489c74c" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/DebtAdditionalInformationDetails" xlink:type="simple" xlink:href="pnr-20251231.xsd#DebtAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/DebtAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_a959ffbb-d89e-41b8-bdf1-27d84551c9df" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_82397e9f-086f-4e6e-9832-1e714f6d84ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a959ffbb-d89e-41b8-bdf1-27d84551c9df" xlink:to="loc_us-gaap_DebtInstrumentTable_82397e9f-086f-4e6e-9832-1e714f6d84ea" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_ae65145c-3de3-4fff-abd1-3f44e4d37471" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_82397e9f-086f-4e6e-9832-1e714f6d84ea" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_ae65145c-3de3-4fff-abd1-3f44e4d37471" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_ae65145c-3de3-4fff-abd1-3f44e4d37471_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_ae65145c-3de3-4fff-abd1-3f44e4d37471" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_ae65145c-3de3-4fff-abd1-3f44e4d37471_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_003e6c8a-07e1-4790-a760-3b476fe17e14" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_ae65145c-3de3-4fff-abd1-3f44e4d37471" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_003e6c8a-07e1-4790-a760-3b476fe17e14" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_9f95c7a0-8eec-4c9c-b5ae-bc1858008105" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_003e6c8a-07e1-4790-a760-3b476fe17e14" xlink:to="loc_us-gaap_LineOfCreditMember_9f95c7a0-8eec-4c9c-b5ae-bc1858008105" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TermLoansMember_7459a62b-9c07-4ee6-b78d-a0dfc7800e0a" xlink:href="pnr-20251231.xsd#pnr_TermLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_003e6c8a-07e1-4790-a760-3b476fe17e14" xlink:to="loc_pnr_TermLoansMember_7459a62b-9c07-4ee6-b78d-a0dfc7800e0a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_7cb47711-5939-4da2-bb11-64aaef410324" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_003e6c8a-07e1-4790-a760-3b476fe17e14" xlink:to="loc_us-gaap_UnsecuredDebtMember_7cb47711-5939-4da2-bb11-64aaef410324" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_0e0b5b75-3a57-4392-9fa0-06af4bf5734c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_82397e9f-086f-4e6e-9832-1e714f6d84ea" xlink:to="loc_us-gaap_CreditFacilityAxis_0e0b5b75-3a57-4392-9fa0-06af4bf5734c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_0e0b5b75-3a57-4392-9fa0-06af4bf5734c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_0e0b5b75-3a57-4392-9fa0-06af4bf5734c" xlink:to="loc_us-gaap_CreditFacilityDomain_0e0b5b75-3a57-4392-9fa0-06af4bf5734c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_f88c50f7-1006-4e70-9706-078fa9cc69ba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_0e0b5b75-3a57-4392-9fa0-06af4bf5734c" xlink:to="loc_us-gaap_CreditFacilityDomain_f88c50f7-1006-4e70-9706-078fa9cc69ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_7e95d664-16c5-4908-9971-4fe261f6e1e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_f88c50f7-1006-4e70-9706-078fa9cc69ba" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_7e95d664-16c5-4908-9971-4fe261f6e1e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_1f480033-b5e2-4f22-9852-6a43ff485d53" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_82397e9f-086f-4e6e-9832-1e714f6d84ea" xlink:to="loc_us-gaap_DebtInstrumentAxis_1f480033-b5e2-4f22-9852-6a43ff485d53" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_1f480033-b5e2-4f22-9852-6a43ff485d53_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_1f480033-b5e2-4f22-9852-6a43ff485d53" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_1f480033-b5e2-4f22-9852-6a43ff485d53_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_2fe38a70-6f33-4dfb-97ee-dbdb7558d4ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_1f480033-b5e2-4f22-9852-6a43ff485d53" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_2fe38a70-6f33-4dfb-97ee-dbdb7558d4ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_A5YearTermLoanFacilityMember_72bb9765-6076-4b34-a506-d4467e77bd33" xlink:href="pnr-20251231.xsd#pnr_A5YearTermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_2fe38a70-6f33-4dfb-97ee-dbdb7558d4ab" xlink:to="loc_pnr_A5YearTermLoanFacilityMember_72bb9765-6076-4b34-a506-d4467e77bd33" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityAxis_26c0663d-8010-4fed-8bfb-ba7840bea582" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_82397e9f-086f-4e6e-9832-1e714f6d84ea" xlink:to="loc_us-gaap_LineOfCreditFacilityAxis_26c0663d-8010-4fed-8bfb-ba7840bea582" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_26c0663d-8010-4fed-8bfb-ba7840bea582_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityLenderDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_26c0663d-8010-4fed-8bfb-ba7840bea582" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_26c0663d-8010-4fed-8bfb-ba7840bea582_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_febf5e5e-8cfc-46e8-b89d-165e051bce8e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityLenderDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_26c0663d-8010-4fed-8bfb-ba7840bea582" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_febf5e5e-8cfc-46e8-b89d-165e051bce8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_OtherCreditFacilitiesMember_974ae3b1-5b75-412e-88a5-69e7eb68204d" xlink:href="pnr-20251231.xsd#pnr_OtherCreditFacilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLenderDomain_febf5e5e-8cfc-46e8-b89d-165e051bce8e" xlink:to="loc_pnr_OtherCreditFacilitiesMember_974ae3b1-5b75-412e-88a5-69e7eb68204d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_6890f067-3765-4d22-93ec-b6b724920a37" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_82397e9f-086f-4e6e-9832-1e714f6d84ea" xlink:to="loc_srt_RangeAxis_6890f067-3765-4d22-93ec-b6b724920a37" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_6890f067-3765-4d22-93ec-b6b724920a37_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_6890f067-3765-4d22-93ec-b6b724920a37" xlink:to="loc_srt_RangeMember_6890f067-3765-4d22-93ec-b6b724920a37_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_f91805c1-64bb-4610-80e4-ef40d9ce0082" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_6890f067-3765-4d22-93ec-b6b724920a37" xlink:to="loc_srt_RangeMember_f91805c1-64bb-4610-80e4-ef40d9ce0082" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_2dc00efb-32c9-4f71-8e45-2e1ffba95c2d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_f91805c1-64bb-4610-80e4-ef40d9ce0082" xlink:to="loc_srt_MinimumMember_2dc00efb-32c9-4f71-8e45-2e1ffba95c2d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_478d5ca7-645e-4b5e-85e5-34aa2a7126bd" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_f91805c1-64bb-4610-80e4-ef40d9ce0082" xlink:to="loc_srt_MaximumMember_478d5ca7-645e-4b5e-85e5-34aa2a7126bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_2835ac26-4f2c-4090-843f-6966c76ff07d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_82397e9f-086f-4e6e-9832-1e714f6d84ea" xlink:to="loc_srt_CounterpartyNameAxis_2835ac26-4f2c-4090-843f-6966c76ff07d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_2835ac26-4f2c-4090-843f-6966c76ff07d_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_2835ac26-4f2c-4090-843f-6966c76ff07d" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_2835ac26-4f2c-4090-843f-6966c76ff07d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_353385eb-4d91-4c14-9e2e-98ea997e1ab1" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_2835ac26-4f2c-4090-843f-6966c76ff07d" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_353385eb-4d91-4c14-9e2e-98ea997e1ab1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_PentairPentairFinanceSRlPFSAMember_6fad3c74-156c-4e0d-924a-2813138f4a17" xlink:href="pnr-20251231.xsd#pnr_PentairPentairFinanceSRlPFSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_353385eb-4d91-4c14-9e2e-98ea997e1ab1" xlink:to="loc_pnr_PentairPentairFinanceSRlPFSAMember_6fad3c74-156c-4e0d-924a-2813138f4a17" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_5720f2c3-1662-4ff5-9f9a-0bfd4c19519c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a959ffbb-d89e-41b8-bdf1-27d84551c9df" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_5720f2c3-1662-4ff5-9f9a-0bfd4c19519c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_2ecdf03a-cb86-4831-b8da-1f4f56353f4c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a959ffbb-d89e-41b8-bdf1-27d84551c9df" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_2ecdf03a-cb86-4831-b8da-1f4f56353f4c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_LineofCreditFacilityAccordionFeatureIncreaseLimit_7828a7fc-2239-4e50-b74b-bbe7da7d9891" xlink:href="pnr-20251231.xsd#pnr_LineofCreditFacilityAccordionFeatureIncreaseLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a959ffbb-d89e-41b8-bdf1-27d84551c9df" xlink:to="loc_pnr_LineofCreditFacilityAccordionFeatureIncreaseLimit_7828a7fc-2239-4e50-b74b-bbe7da7d9891" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_8a56869f-dac0-4046-b4e4-f354949a154d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a959ffbb-d89e-41b8-bdf1-27d84551c9df" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_8a56869f-dac0-4046-b4e4-f354949a154d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentPeriodicPayment_3bd964bf-4aff-4e3b-9d0d-1269c88d3328" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentPeriodicPayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a959ffbb-d89e-41b8-bdf1-27d84551c9df" xlink:to="loc_us-gaap_DebtInstrumentPeriodicPayment_3bd964bf-4aff-4e3b-9d0d-1269c88d3328" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLongTermDebt_861a5b56-0d5d-4889-9382-4e87d7924d2f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RepaymentsOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a959ffbb-d89e-41b8-bdf1-27d84551c9df" xlink:to="loc_us-gaap_RepaymentsOfLongTermDebt_861a5b56-0d5d-4889-9382-4e87d7924d2f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DebtInstrumentCovenantUnrestrictedCash_8861ffee-2739-4af0-81e6-e987b6fd7187" xlink:href="pnr-20251231.xsd#pnr_DebtInstrumentCovenantUnrestrictedCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a959ffbb-d89e-41b8-bdf1-27d84551c9df" xlink:to="loc_pnr_DebtInstrumentCovenantUnrestrictedCash_8861ffee-2739-4af0-81e6-e987b6fd7187" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DebtInstrumentLeverageRatioCovenant_60717613-da91-436c-8009-70a21c21f78e" xlink:href="pnr-20251231.xsd#pnr_DebtInstrumentLeverageRatioCovenant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a959ffbb-d89e-41b8-bdf1-27d84551c9df" xlink:to="loc_pnr_DebtInstrumentLeverageRatioCovenant_60717613-da91-436c-8009-70a21c21f78e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DebtInstrumentCovenantNumberOfTestingPeriods_33b9578d-5642-471a-8cf2-cc45da4078d0" xlink:href="pnr-20251231.xsd#pnr_DebtInstrumentCovenantNumberOfTestingPeriods"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a959ffbb-d89e-41b8-bdf1-27d84551c9df" xlink:to="loc_pnr_DebtInstrumentCovenantNumberOfTestingPeriods_33b9578d-5642-471a-8cf2-cc45da4078d0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DebtInstrumentEBITDARatioCovenant_59e98749-9b75-46ca-ad2a-cff85c0a7cc4" xlink:href="pnr-20251231.xsd#pnr_DebtInstrumentEBITDARatioCovenant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a959ffbb-d89e-41b8-bdf1-27d84551c9df" xlink:to="loc_pnr_DebtInstrumentEBITDARatioCovenant_59e98749-9b75-46ca-ad2a-cff85c0a7cc4" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_0c22875e-d7c1-4bb0-bab6-5312da7f45b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a959ffbb-d89e-41b8-bdf1-27d84551c9df" xlink:to="loc_us-gaap_LineOfCredit_0c22875e-d7c1-4bb0-bab6-5312da7f45b6" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_LongTermDebtMaturityYearOneTermLoanFacilityPayments_d809d5b3-904b-4d1a-9d03-4f47220f745e" xlink:href="pnr-20251231.xsd#pnr_LongTermDebtMaturityYearOneTermLoanFacilityPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a959ffbb-d89e-41b8-bdf1-27d84551c9df" xlink:to="loc_pnr_LongTermDebtMaturityYearOneTermLoanFacilityPayments_d809d5b3-904b-4d1a-9d03-4f47220f745e" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/DerivativesandFinancialInstrumentsAdditionalInformationDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#DerivativesandFinancialInstrumentsAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/DerivativesandFinancialInstrumentsAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureLineItems_a62c50b8-9c1e-4429-90a9-ead34c42253f" xlink:href="pnr-20251231.xsd#pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureTable_51945270-5ebe-4098-9e97-0c1ed71d00e6" xlink:href="pnr-20251231.xsd#pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureLineItems_a62c50b8-9c1e-4429-90a9-ead34c42253f" xlink:to="loc_pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureTable_51945270-5ebe-4098-9e97-0c1ed71d00e6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_2e5b5dac-3847-485c-94d0-f6515c678ff9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureTable_51945270-5ebe-4098-9e97-0c1ed71d00e6" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_2e5b5dac-3847-485c-94d0-f6515c678ff9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_2e5b5dac-3847-485c-94d0-f6515c678ff9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_2e5b5dac-3847-485c-94d0-f6515c678ff9" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_2e5b5dac-3847-485c-94d0-f6515c678ff9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_ab6d46b1-f39f-44e9-8f84-942cbafb1687" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_2e5b5dac-3847-485c-94d0-f6515c678ff9" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_ab6d46b1-f39f-44e9-8f84-942cbafb1687" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_93ec0eb2-01da-450e-994b-ed6343ac1b79" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_ab6d46b1-f39f-44e9-8f84-942cbafb1687" xlink:to="loc_us-gaap_ForeignExchangeContractMember_93ec0eb2-01da-450e-994b-ed6343ac1b79" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CurrencySwapMember_3f52af50-b898-4010-afcd-4e724357dddb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CurrencySwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_ab6d46b1-f39f-44e9-8f84-942cbafb1687" xlink:to="loc_us-gaap_CurrencySwapMember_3f52af50-b898-4010-afcd-4e724357dddb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019b0f50-74c2-72a9-a597-b99ffc744ba9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_ab6d46b1-f39f-44e9-8f84-942cbafb1687" xlink:to="loc_us-gaap_CashFlowHedgingMember_019b0f50-74c2-72a9-a597-b99ffc744ba9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_InterestRateSwapAndInterestRateCollarMember_b88c3e9c-877b-4411-92ef-be76fcb5865e" xlink:href="pnr-20251231.xsd#pnr_InterestRateSwapAndInterestRateCollarMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_ab6d46b1-f39f-44e9-8f84-942cbafb1687" xlink:to="loc_pnr_InterestRateSwapAndInterestRateCollarMember_b88c3e9c-877b-4411-92ef-be76fcb5865e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_6343b7e1-f297-4aec-965e-c64cbacab394" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_InterestRateSwapAndInterestRateCollarMember_b88c3e9c-877b-4411-92ef-be76fcb5865e" xlink:to="loc_us-gaap_InterestRateSwapMember_6343b7e1-f297-4aec-965e-c64cbacab394" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_InterestRateCollarMember_204928a4-8302-48b7-b708-f926ece40818" xlink:href="pnr-20251231.xsd#pnr_InterestRateCollarMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_InterestRateSwapAndInterestRateCollarMember_b88c3e9c-877b-4411-92ef-be76fcb5865e" xlink:to="loc_pnr_InterestRateCollarMember_204928a4-8302-48b7-b708-f926ece40818" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_50a09915-a874-424b-85a1-6ba8a153ddc3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureTable_51945270-5ebe-4098-9e97-0c1ed71d00e6" xlink:to="loc_srt_RangeAxis_50a09915-a874-424b-85a1-6ba8a153ddc3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_50a09915-a874-424b-85a1-6ba8a153ddc3_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_50a09915-a874-424b-85a1-6ba8a153ddc3" xlink:to="loc_srt_RangeMember_50a09915-a874-424b-85a1-6ba8a153ddc3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_254905e2-ce91-404b-b0ec-150818440a79" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_50a09915-a874-424b-85a1-6ba8a153ddc3" xlink:to="loc_srt_RangeMember_254905e2-ce91-404b-b0ec-150818440a79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_46e57f86-bc67-46bb-a3aa-67e33ab4d56c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_254905e2-ce91-404b-b0ec-150818440a79" xlink:to="loc_srt_MinimumMember_46e57f86-bc67-46bb-a3aa-67e33ab4d56c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_7186261b-8ff0-4abd-9d71-213d54f68c5e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_254905e2-ce91-404b-b0ec-150818440a79" xlink:to="loc_srt_MaximumMember_7186261b-8ff0-4abd-9d71-213d54f68c5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_7abfb719-124a-48ba-9f0f-81dd5116c5b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureTable_51945270-5ebe-4098-9e97-0c1ed71d00e6" xlink:to="loc_us-gaap_DebtInstrumentAxis_7abfb719-124a-48ba-9f0f-81dd5116c5b8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_7abfb719-124a-48ba-9f0f-81dd5116c5b8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_7abfb719-124a-48ba-9f0f-81dd5116c5b8" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_7abfb719-124a-48ba-9f0f-81dd5116c5b8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_3b48179e-11c9-49b3-ba54-0382a618db3b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_7abfb719-124a-48ba-9f0f-81dd5116c5b8" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_3b48179e-11c9-49b3-ba54-0382a618db3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_A5YearTermLoanFacilityMember_24fa8283-4dfa-41f4-9a7e-16cab5b9662b" xlink:href="pnr-20251231.xsd#pnr_A5YearTermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_3b48179e-11c9-49b3-ba54-0382a618db3b" xlink:to="loc_pnr_A5YearTermLoanFacilityMember_24fa8283-4dfa-41f4-9a7e-16cab5b9662b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_01a83d7e-9b9d-48f8-84b8-5d4f36a34b8e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureTable_51945270-5ebe-4098-9e97-0c1ed71d00e6" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_01a83d7e-9b9d-48f8-84b8-5d4f36a34b8e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_01a83d7e-9b9d-48f8-84b8-5d4f36a34b8e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_01a83d7e-9b9d-48f8-84b8-5d4f36a34b8e" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_01a83d7e-9b9d-48f8-84b8-5d4f36a34b8e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_56e77376-8cff-49ce-a6f3-87c332459c00" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_01a83d7e-9b9d-48f8-84b8-5d4f36a34b8e" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_56e77376-8cff-49ce-a6f3-87c332459c00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_09c824c6-e067-480f-ae56-0b3db1389b4d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_56e77376-8cff-49ce-a6f3-87c332459c00" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_09c824c6-e067-480f-ae56-0b3db1389b4d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_af334bcf-11b5-4109-9b3c-76c55b10be1e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureLineItems_a62c50b8-9c1e-4429-90a9-ead34c42253f" xlink:to="loc_us-gaap_DerivativeNotionalAmount_af334bcf-11b5-4109-9b3c-76c55b10be1e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TranslationAdjustmentForNetInvestmentHedgeIncreaseDecreaseNetOfTax_9b31f0e3-a2d7-4277-b658-3c1953b382f3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TranslationAdjustmentForNetInvestmentHedgeIncreaseDecreaseNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureLineItems_a62c50b8-9c1e-4429-90a9-ead34c42253f" xlink:to="loc_us-gaap_TranslationAdjustmentForNetInvestmentHedgeIncreaseDecreaseNetOfTax_9b31f0e3-a2d7-4277-b658-3c1953b382f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_PaymentsFromHedge_a0fc4235-fd39-45da-927c-62f87e35a988" xlink:href="pnr-20251231.xsd#pnr_PaymentsFromHedge"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureLineItems_a62c50b8-9c1e-4429-90a9-ead34c42253f" xlink:to="loc_pnr_PaymentsFromHedge_a0fc4235-fd39-45da-927c-62f87e35a988" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForHedgeFinancingActivities_d27f9474-04b2-4207-ad70-86fb866906ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsForHedgeFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureLineItems_a62c50b8-9c1e-4429-90a9-ead34c42253f" xlink:to="loc_us-gaap_PaymentsForHedgeFinancingActivities_d27f9474-04b2-4207-ad70-86fb866906ef" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeOperating_87201830-b7f2-4774-b5f6-fca1d724140d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestIncomeOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureLineItems_a62c50b8-9c1e-4429-90a9-ead34c42253f" xlink:to="loc_us-gaap_InterestIncomeOperating_87201830-b7f2-4774-b5f6-fca1d724140d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromHedgeInvestingActivities_f4ac8e60-d91a-4e09-998c-2c148acb262a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromHedgeInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureLineItems_a62c50b8-9c1e-4429-90a9-ead34c42253f" xlink:to="loc_us-gaap_ProceedsFromHedgeInvestingActivities_f4ac8e60-d91a-4e09-998c-2c148acb262a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_ProceedsFromHedge_04717c77-d9c7-4824-977f-cacbe3efd0a1" xlink:href="pnr-20251231.xsd#pnr_ProceedsFromHedge"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureLineItems_a62c50b8-9c1e-4429-90a9-ead34c42253f" xlink:to="loc_pnr_ProceedsFromHedge_04717c77-d9c7-4824-977f-cacbe3efd0a1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForHedgeInvestingActivities_4a8613d8-aa90-41e0-b345-c959dd54bebe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsForHedgeInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureLineItems_a62c50b8-9c1e-4429-90a9-ead34c42253f" xlink:to="loc_us-gaap_PaymentsForHedgeInvestingActivities_4a8613d8-aa90-41e0-b345-c959dd54bebe" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AociLossCashFlowHedgeCumulativeGainLossAfterTax_124bc39f-af87-48a0-bc7c-687deb7f8737" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AociLossCashFlowHedgeCumulativeGainLossAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureLineItems_a62c50b8-9c1e-4429-90a9-ead34c42253f" xlink:to="loc_us-gaap_AociLossCashFlowHedgeCumulativeGainLossAfterTax_124bc39f-af87-48a0-bc7c-687deb7f8737" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_ContingentEarnOutLiabilitiesFairValueDisclosure_46de23d7-96e8-4cd8-abd2-1ecc1868de48" xlink:href="pnr-20251231.xsd#pnr_ContingentEarnOutLiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_DerivativeInstrumentsAndHedgingActivitiesDisclosureLineItems_a62c50b8-9c1e-4429-90a9-ead34c42253f" xlink:to="loc_pnr_ContingentEarnOutLiabilitiesFairValueDisclosure_46de23d7-96e8-4cd8-abd2-1ecc1868de48" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/DerivativesandFinancialInstrumentsRecordedAmountsandEstimatedFairValuesofLongtermDebtandDerivativeFinancialInstrumentsDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#DerivativesandFinancialInstrumentsRecordedAmountsandEstimatedFairValuesofLongtermDebtandDerivativeFinancialInstrumentsDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/DerivativesandFinancialInstrumentsRecordedAmountsandEstimatedFairValuesofLongtermDebtandDerivativeFinancialInstrumentsDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_90d59fb5-70f0-4329-b171-4c1d9385091f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_a0951c91-4284-4bca-91bf-ecf2a6d0a92e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_90d59fb5-70f0-4329-b171-4c1d9385091f" xlink:to="loc_us-gaap_DerivativeTable_a0951c91-4284-4bca-91bf-ecf2a6d0a92e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_31b8e701-1653-4d30-ae5f-5653d5e00f37" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_a0951c91-4284-4bca-91bf-ecf2a6d0a92e" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_31b8e701-1653-4d30-ae5f-5653d5e00f37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_31b8e701-1653-4d30-ae5f-5653d5e00f37_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_31b8e701-1653-4d30-ae5f-5653d5e00f37" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_31b8e701-1653-4d30-ae5f-5653d5e00f37_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_34b635a0-0405-4f08-9da7-377b89906ff3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_31b8e701-1653-4d30-ae5f-5653d5e00f37" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_34b635a0-0405-4f08-9da7-377b89906ff3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_df88153d-036e-44e1-a0be-efdc7c447495" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_34b635a0-0405-4f08-9da7-377b89906ff3" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_df88153d-036e-44e1-a0be-efdc7c447495" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_99fe988c-86ed-4e76-946b-61a151fb40f4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_df88153d-036e-44e1-a0be-efdc7c447495" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_99fe988c-86ed-4e76-946b-61a151fb40f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_a59d3201-cb04-4282-8f50-d588087b8d0a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_df88153d-036e-44e1-a0be-efdc7c447495" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_a59d3201-cb04-4282-8f50-d588087b8d0a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtPercentageBearingVariableInterestAmount_d81fcfe1-2a23-4887-95cf-abe4d8c4469c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtPercentageBearingVariableInterestAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_90d59fb5-70f0-4329-b171-4c1d9385091f" xlink:to="loc_us-gaap_LongtermDebtPercentageBearingVariableInterestAmount_d81fcfe1-2a23-4887-95cf-abe4d8c4469c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtPercentageBearingFixedInterestAmount_b6220e16-e4d3-4b79-a4be-6271d1222339" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtPercentageBearingFixedInterestAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_90d59fb5-70f0-4329-b171-4c1d9385091f" xlink:to="loc_us-gaap_LongtermDebtPercentageBearingFixedInterestAmount_b6220e16-e4d3-4b79-a4be-6271d1222339" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_bdc9ed67-be55-4d4e-8634-362757b91624" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_90d59fb5-70f0-4329-b171-4c1d9385091f" xlink:to="loc_us-gaap_LongTermDebt_bdc9ed67-be55-4d4e-8634-362757b91624" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/DerivativesandFinancialInstrumentsAssetsandLiabilitiesMeasuredatFairValueDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#DerivativesandFinancialInstrumentsAssetsandLiabilitiesMeasuredatFairValueDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/DerivativesandFinancialInstrumentsAssetsandLiabilitiesMeasuredatFairValueDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2e5fc745-8e26-41e5-a907-950963b330a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_88f8d68b-955b-405d-9fa5-6aba789daf8e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2e5fc745-8e26-41e5-a907-950963b330a4" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_88f8d68b-955b-405d-9fa5-6aba789daf8e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_f70b1819-5226-4f5e-b185-d5f5916257a8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_88f8d68b-955b-405d-9fa5-6aba789daf8e" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_f70b1819-5226-4f5e-b185-d5f5916257a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f70b1819-5226-4f5e-b185-d5f5916257a8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_f70b1819-5226-4f5e-b185-d5f5916257a8" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f70b1819-5226-4f5e-b185-d5f5916257a8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ee4bbf9f-2282-401f-8826-69827f54bf65" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_f70b1819-5226-4f5e-b185-d5f5916257a8" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ee4bbf9f-2282-401f-8826-69827f54bf65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_ee48110e-7177-4949-a340-e17fc726fa09" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ee4bbf9f-2282-401f-8826-69827f54bf65" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_ee48110e-7177-4949-a340-e17fc726fa09" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_c1c1bffd-c182-49b5-9d93-a717624082f5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ee4bbf9f-2282-401f-8826-69827f54bf65" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_c1c1bffd-c182-49b5-9d93-a717624082f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_b91f2f4b-a014-4874-9c50-ec6f8e9c616f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ee4bbf9f-2282-401f-8826-69827f54bf65" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_b91f2f4b-a014-4874-9c50-ec6f8e9c616f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember_75ae7911-1e86-4c0e-a09c-7374ebc5732d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ee4bbf9f-2282-401f-8826-69827f54bf65" xlink:to="loc_us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember_75ae7911-1e86-4c0e-a09c-7374ebc5732d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_1060afec-95c6-4960-b468-65bfe02cf54d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_88f8d68b-955b-405d-9fa5-6aba789daf8e" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_1060afec-95c6-4960-b468-65bfe02cf54d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_1060afec-95c6-4960-b468-65bfe02cf54d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_1060afec-95c6-4960-b468-65bfe02cf54d" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_1060afec-95c6-4960-b468-65bfe02cf54d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_af994369-dac9-44ff-a904-75aca1d89b6c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_1060afec-95c6-4960-b468-65bfe02cf54d" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_af994369-dac9-44ff-a904-75aca1d89b6c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_1f33e3c8-0eee-4f15-8abf-15157a64d363" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_af994369-dac9-44ff-a904-75aca1d89b6c" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_1f33e3c8-0eee-4f15-8abf-15157a64d363" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_396d0678-f888-4c36-9cd1-41e5d276ca3c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_88f8d68b-955b-405d-9fa5-6aba789daf8e" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_396d0678-f888-4c36-9cd1-41e5d276ca3c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_396d0678-f888-4c36-9cd1-41e5d276ca3c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_396d0678-f888-4c36-9cd1-41e5d276ca3c" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_396d0678-f888-4c36-9cd1-41e5d276ca3c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_0c200b36-2d4c-4374-8dde-d87534a22dfc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_396d0678-f888-4c36-9cd1-41e5d276ca3c" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_0c200b36-2d4c-4374-8dde-d87534a22dfc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateContractMember_495292b5-7102-410a-89e1-52c46e6fba73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_0c200b36-2d4c-4374-8dde-d87534a22dfc" xlink:to="loc_us-gaap_InterestRateContractMember_495292b5-7102-410a-89e1-52c46e6fba73" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_019c531f-a7f0-74b7-89fb-00bf8216d244" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2e5fc745-8e26-41e5-a907-950963b330a4" xlink:to="loc_us-gaap_DerivativeLiabilities_019c531f-a7f0-74b7-89fb-00bf8216d244" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_03ade6ff-3ca8-45cb-b3ba-e0d8dacf17fd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2e5fc745-8e26-41e5-a907-950963b330a4" xlink:to="loc_us-gaap_DerivativeAssets_03ade6ff-3ca8-45cb-b3ba-e0d8dacf17fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyContractAssetFairValueDisclosure_4e6b9fe5-d8fd-4e0b-8282-c1052e411017" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignCurrencyContractAssetFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2e5fc745-8e26-41e5-a907-950963b330a4" xlink:to="loc_us-gaap_ForeignCurrencyContractAssetFairValueDisclosure_4e6b9fe5-d8fd-4e0b-8282-c1052e411017" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure_be4d9f7a-23d3-477c-916e-3ce023a74d76" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2e5fc745-8e26-41e5-a907-950963b330a4" xlink:to="loc_us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure_be4d9f7a-23d3-477c-916e-3ce023a74d76" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DeferredCompensationPlanAssetsFairValueDisclosure_00dbc2de-3f43-4ed7-b380-9792747528ed" xlink:href="pnr-20251231.xsd#pnr_DeferredCompensationPlanAssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2e5fc745-8e26-41e5-a907-950963b330a4" xlink:to="loc_pnr_DeferredCompensationPlanAssetsFairValueDisclosure_00dbc2de-3f43-4ed7-b380-9792747528ed" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_ContingentEarnOutLiabilitiesFairValueDisclosure_f3a3aa36-8bf1-4cbe-974b-c7728471aa25" xlink:href="pnr-20251231.xsd#pnr_ContingentEarnOutLiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2e5fc745-8e26-41e5-a907-950963b330a4" xlink:to="loc_pnr_ContingentEarnOutLiabilitiesFairValueDisclosure_f3a3aa36-8bf1-4cbe-974b-c7728471aa25" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetAssetLiability_ca2ac061-a44c-43e0-8686-d91e5b1e03a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueNetAssetLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2e5fc745-8e26-41e5-a907-950963b330a4" xlink:to="loc_us-gaap_FairValueNetAssetLiability_ca2ac061-a44c-43e0-8686-d91e5b1e03a7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfIntangibleAssetsExcludingGoodwill_019c6827-4c2a-7088-8b68-a2ebb77943df" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ImpairmentOfIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2e5fc745-8e26-41e5-a907-950963b330a4" xlink:to="loc_us-gaap_ImpairmentOfIntangibleAssetsExcludingGoodwill_019c6827-4c2a-7088-8b68-a2ebb77943df" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/IncomeTaxesReconciliationofFederalStatutoryIncomeTaxRate2025Detail" xlink:type="simple" xlink:href="pnr-20251231.xsd#IncomeTaxesReconciliationofFederalStatutoryIncomeTaxRate2025Detail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/IncomeTaxesReconciliationofFederalStatutoryIncomeTaxRate2025Detail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019b2d85-df99-72b3-b33e-e4919622a5aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019b2d85-df99-7497-92d0-d9dc34f2695c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019b2d85-df99-72b3-b33e-e4919622a5aa" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019b2d85-df99-7497-92d0-d9dc34f2695c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_019c5859-028c-71d8-a17c-3b5adcc2a401" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019b2d85-df99-7497-92d0-d9dc34f2695c" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_019c5859-028c-71d8-a17c-3b5adcc2a401" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019c5859-028c-71d8-a17c-3b5adcc2a401_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019c5859-028c-71d8-a17c-3b5adcc2a401" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019c5859-028c-71d8-a17c-3b5adcc2a401_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019c5859-028c-7d43-bec6-37b197f796ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019c5859-028c-71d8-a17c-3b5adcc2a401" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019c5859-028c-7d43-bec6-37b197f796ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCountryMember_019c683a-906e-757d-8aac-5d3662a0d0e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019c5859-028c-7d43-bec6-37b197f796ef" xlink:to="loc_us-gaap_ForeignCountryMember_019c683a-906e-757d-8aac-5d3662a0d0e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CH_019c5859-6fb8-7f8b-96e4-ec6a861b6c68" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_CH"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019c683a-906e-757d-8aac-5d3662a0d0e5" xlink:to="loc_country_CH_019c5859-6fb8-7f8b-96e4-ec6a861b6c68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignTaxJurisdictionOtherMember_019c586b-a7ea-73cc-9b27-e693c7bffa92" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignTaxJurisdictionOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019c683a-906e-757d-8aac-5d3662a0d0e5" xlink:to="loc_us-gaap_ForeignTaxJurisdictionOtherMember_019c586b-a7ea-73cc-9b27-e693c7bffa92" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticCountryMember_019c683a-df31-7780-babb-e8f048a34cf8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DomesticCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019c5859-028c-7d43-bec6-37b197f796ef" xlink:to="loc_us-gaap_DomesticCountryMember_019c683a-df31-7780-babb-e8f048a34cf8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_019c5861-177e-70d5-a0cc-0b7e9a58da23" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DomesticCountryMember_019c683a-df31-7780-babb-e8f048a34cf8" xlink:to="loc_country_US_019c5861-177e-70d5-a0cc-0b7e9a58da23" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019c6832-d295-7e03-b8e7-33b4760ede7d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019b2d85-df99-72b3-b33e-e4919622a5aa" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019c6832-d295-7e03-b8e7-33b4760ede7d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate_019b2d85-df99-718c-92ad-c6a1f0e6b1be" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019c6832-d295-7e03-b8e7-33b4760ede7d" xlink:to="loc_us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate_019b2d85-df99-718c-92ad-c6a1f0e6b1be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationForeignIncomeTaxRateDifferential_019c4efe-403d-7d3d-b7e7-db1ecb22291b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxReconciliationForeignIncomeTaxRateDifferential"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019c6832-d295-7e03-b8e7-33b4760ede7d" xlink:to="loc_us-gaap_IncomeTaxReconciliationForeignIncomeTaxRateDifferential_019c4efe-403d-7d3d-b7e7-db1ecb22291b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_EffectiveIncomeTaxRateReconciliationPartnershipImpactsAmount_019c5879-f298-790a-a03e-f32bdf4fc9e4" xlink:href="pnr-20251231.xsd#pnr_EffectiveIncomeTaxRateReconciliationPartnershipImpactsAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019c6832-d295-7e03-b8e7-33b4760ede7d" xlink:to="loc_pnr_EffectiveIncomeTaxRateReconciliationPartnershipImpactsAmount_019c5879-f298-790a-a03e-f32bdf4fc9e4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_EffectiveIncomeTaxRateReconciliationCantonalIncomeTaxesPercent_019c7cce-9d6c-7a63-a842-966f8d0e97b6" xlink:href="pnr-20251231.xsd#pnr_EffectiveIncomeTaxRateReconciliationCantonalIncomeTaxesPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019c6832-d295-7e03-b8e7-33b4760ede7d" xlink:to="loc_pnr_EffectiveIncomeTaxRateReconciliationCantonalIncomeTaxesPercent_019c7cce-9d6c-7a63-a842-966f8d0e97b6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_EffectiveIncomeTaxRateReconciliationCantonalIncomeTaxesAmount_019c7ccd-0a51-7f5e-99fe-2e98366ebdad" xlink:href="pnr-20251231.xsd#pnr_EffectiveIncomeTaxRateReconciliationCantonalIncomeTaxesAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019c6832-d295-7e03-b8e7-33b4760ede7d" xlink:to="loc_pnr_EffectiveIncomeTaxRateReconciliationCantonalIncomeTaxesAmount_019c7ccd-0a51-7f5e-99fe-2e98366ebdad" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes_019c4f04-19fc-74a0-b069-89f9d5d8b39d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019c6832-d295-7e03-b8e7-33b4760ede7d" xlink:to="loc_us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes_019c4f04-19fc-74a0-b069-89f9d5d8b39d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationCrossBorderOtherAmount_019c4f01-35f6-72b4-88da-3d7231ebe115" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationCrossBorderOtherAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019c6832-d295-7e03-b8e7-33b4760ede7d" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationCrossBorderOtherAmount_019c4f01-35f6-72b4-88da-3d7231ebe115" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationShareBasedCompensationExcessTaxBenefitAmount_019c5866-1763-73ec-9145-81cefaf1b3b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationShareBasedCompensationExcessTaxBenefitAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019c6832-d295-7e03-b8e7-33b4760ede7d" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationShareBasedCompensationExcessTaxBenefitAmount_019c5866-1763-73ec-9145-81cefaf1b3b0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationOtherAdjustments_019c586e-8e2a-7290-be79-429f2d1e10e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxReconciliationOtherAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019c6832-d295-7e03-b8e7-33b4760ede7d" xlink:to="loc_us-gaap_IncomeTaxReconciliationOtherAdjustments_019c586e-8e2a-7290-be79-429f2d1e10e5" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_EffectiveIncomeTaxRateReconciliationUnrecognizedTaxBenefitsChangeInPriorYearAmount_019c5882-6429-779b-9f2f-60b6c0d2c3f7" xlink:href="pnr-20251231.xsd#pnr_EffectiveIncomeTaxRateReconciliationUnrecognizedTaxBenefitsChangeInPriorYearAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019c6832-d295-7e03-b8e7-33b4760ede7d" xlink:to="loc_pnr_EffectiveIncomeTaxRateReconciliationUnrecognizedTaxBenefitsChangeInPriorYearAmount_019c5882-6429-779b-9f2f-60b6c0d2c3f7" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019c5874-dd4d-71db-b934-5b3361722616" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019c6832-d295-7e03-b8e7-33b4760ede7d" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019c5874-dd4d-71db-b934-5b3361722616" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019c6833-4178-713a-b850-b06a9800acdd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019b2d85-df99-72b3-b33e-e4919622a5aa" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019c6833-4178-713a-b850-b06a9800acdd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_019b2d87-387f-7cbd-8bfc-6437be88bcae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019c6833-4178-713a-b850-b06a9800acdd" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_019b2d87-387f-7cbd-8bfc-6437be88bcae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential_019c585c-5b9a-7a0a-b963-d844f9db5582" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019c6833-4178-713a-b850-b06a9800acdd" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential_019c585c-5b9a-7a0a-b963-d844f9db5582" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_EffectiveIncomeTaxRateReconciliationPartnershipImpactsPercent_019c587b-33ad-7903-912c-801edd3b80e4" xlink:href="pnr-20251231.xsd#pnr_EffectiveIncomeTaxRateReconciliationPartnershipImpactsPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019c6833-4178-713a-b850-b06a9800acdd" xlink:to="loc_pnr_EffectiveIncomeTaxRateReconciliationPartnershipImpactsPercent_019c587b-33ad-7903-912c-801edd3b80e4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes_019c585e-b71f-7cc3-b726-da4f307dc11a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019c6833-4178-713a-b850-b06a9800acdd" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes_019c585e-b71f-7cc3-b726-da4f307dc11a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationCrossBorderOtherPercent_019c4f02-19f7-7b43-a7d2-7671adb20b1e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationCrossBorderOtherPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019c6833-4178-713a-b850-b06a9800acdd" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationCrossBorderOtherPercent_019c4f02-19f7-7b43-a7d2-7671adb20b1e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationShareBasedCompensationExcessTaxBenefitPercent_019c5868-1d39-7f51-b836-70ea4c2af548" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationShareBasedCompensationExcessTaxBenefitPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019c6833-4178-713a-b850-b06a9800acdd" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationShareBasedCompensationExcessTaxBenefitPercent_019c5868-1d39-7f51-b836-70ea4c2af548" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments_019c586f-5222-7c32-bf0b-3161d35e28d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019c6833-4178-713a-b850-b06a9800acdd" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments_019c586f-5222-7c32-bf0b-3161d35e28d4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_EffectiveIncomeTaxRateReconciliationUnrecognizedTaxBenefitsChangeInPriorYearPercent_019c5883-10c3-7f48-a9de-57274f4ac43a" xlink:href="pnr-20251231.xsd#pnr_EffectiveIncomeTaxRateReconciliationUnrecognizedTaxBenefitsChangeInPriorYearPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019c6833-4178-713a-b850-b06a9800acdd" xlink:to="loc_pnr_EffectiveIncomeTaxRateReconciliationUnrecognizedTaxBenefitsChangeInPriorYearPercent_019c5883-10c3-7f48-a9de-57274f4ac43a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_019c5876-37ae-7c09-b7c4-6f7d4312c86b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019c6833-4178-713a-b850-b06a9800acdd" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_019c5876-37ae-7c09-b7c4-6f7d4312c86b" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/IncomeTaxesIncomeTaxesPaidNetDetails" xlink:type="simple" xlink:href="pnr-20251231.xsd#IncomeTaxesIncomeTaxesPaidNetDetails"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/IncomeTaxesIncomeTaxesPaidNetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems_019c6840-9b6d-781a-a96d-20c2ef0ec19f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionTable_019c6840-9b6d-79c4-9a97-87c32903ff79" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxPaidByIndividualJurisdictionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems_019c6840-9b6d-781a-a96d-20c2ef0ec19f" xlink:to="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionTable_019c6840-9b6d-79c4-9a97-87c32903ff79" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_019c6840-9b6d-7756-9533-df2fb4850147" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionTable_019c6840-9b6d-79c4-9a97-87c32903ff79" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_019c6840-9b6d-7756-9533-df2fb4850147" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019c6840-9b6d-7756-9533-df2fb4850147_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019c6840-9b6d-7756-9533-df2fb4850147" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019c6840-9b6d-7756-9533-df2fb4850147_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019c6840-9b6d-7ad1-ba64-eb123e6ba3ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019c6840-9b6d-7756-9533-df2fb4850147" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019c6840-9b6d-7ad1-ba64-eb123e6ba3ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCountryMember_019c6841-0b4c-7883-9ae6-347e292f9100" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019c6840-9b6d-7ad1-ba64-eb123e6ba3ff" xlink:to="loc_us-gaap_ForeignCountryMember_019c6841-0b4c-7883-9ae6-347e292f9100" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_AU_019c6840-9b6d-79a4-bdd0-4153974acb94" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_AU"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019c6841-0b4c-7883-9ae6-347e292f9100" xlink:to="loc_country_AU_019c6840-9b6d-79a4-bdd0-4153974acb94" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CN_019c6840-bc81-7d22-ba6d-efff1c5fbcb4" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_CN"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019c6841-0b4c-7883-9ae6-347e292f9100" xlink:to="loc_country_CN_019c6840-bc81-7d22-ba6d-efff1c5fbcb4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_DE_019c6840-bc81-70cb-ab50-fcc21a321e08" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_DE"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019c6841-0b4c-7883-9ae6-347e292f9100" xlink:to="loc_country_DE_019c6840-bc81-70cb-ab50-fcc21a321e08" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_IN_019c6840-bc81-76a1-9124-d9140ccaf4d9" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_IN"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019c6841-0b4c-7883-9ae6-347e292f9100" xlink:to="loc_country_IN_019c6840-bc81-76a1-9124-d9140ccaf4d9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CH_019c6840-bc81-7d94-ae2a-ab9835234f0b" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_CH"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019c6841-0b4c-7883-9ae6-347e292f9100" xlink:to="loc_country_CH_019c6840-bc81-7d94-ae2a-ab9835234f0b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignTaxJurisdictionOtherMember_019c6840-bc81-771e-8abf-6ce17e506db8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignTaxJurisdictionOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019c6841-0b4c-7883-9ae6-347e292f9100" xlink:to="loc_us-gaap_ForeignTaxJurisdictionOtherMember_019c6840-bc81-771e-8abf-6ce17e506db8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticCountryMember_019c6844-37aa-7862-b7dd-a2d167b719de" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DomesticCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019c6840-9b6d-7ad1-ba64-eb123e6ba3ff" xlink:to="loc_us-gaap_DomesticCountryMember_019c6844-37aa-7862-b7dd-a2d167b719de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_019c6840-bc81-7de8-986f-060e0d9013b9" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DomesticCountryMember_019c6844-37aa-7862-b7dd-a2d167b719de" xlink:to="loc_country_US_019c6840-bc81-7de8-986f-060e0d9013b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesPaidNet_019c6840-9b6d-7eec-9def-954f178f6436" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxesPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems_019c6840-9b6d-781a-a96d-20c2ef0ec19f" xlink:to="loc_us-gaap_IncomeTaxesPaidNet_019c6840-9b6d-7eec-9def-954f178f6436" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/BenefitPlansObligationsandFundedStatusDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#BenefitPlansObligationsandFundedStatusDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/BenefitPlansObligationsandFundedStatusDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_1d8c77d1-650e-438c-bf90-e560cb60b403" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_833a4510-219a-4be8-9d74-0383e7c9633c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_1d8c77d1-650e-438c-bf90-e560cb60b403" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_833a4510-219a-4be8-9d74-0383e7c9633c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_97a10181-9371-40e5-bdd9-e00d61a2b56f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_833a4510-219a-4be8-9d74-0383e7c9633c" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_97a10181-9371-40e5-bdd9-e00d61a2b56f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_97a10181-9371-40e5-bdd9-e00d61a2b56f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_97a10181-9371-40e5-bdd9-e00d61a2b56f" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_97a10181-9371-40e5-bdd9-e00d61a2b56f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_b0b34067-e4fc-49e4-a38e-b33501681a00" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_97a10181-9371-40e5-bdd9-e00d61a2b56f" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_b0b34067-e4fc-49e4-a38e-b33501681a00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_95bf6b15-9286-465e-98ae-03e279a8c319" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_b0b34067-e4fc-49e4-a38e-b33501681a00" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_95bf6b15-9286-465e-98ae-03e279a8c319" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_5dbd0ceb-69cb-463b-9268-445effe5ab79" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_b0b34067-e4fc-49e4-a38e-b33501681a00" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_5dbd0ceb-69cb-463b-9268-445effe5ab79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward_13b2505f-d21f-4025-8a92-25f4825d6bfb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_1d8c77d1-650e-438c-bf90-e560cb60b403" xlink:to="loc_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward_13b2505f-d21f-4025-8a92-25f4825d6bfb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanBenefitObligation_8896290c-eae7-4722-be24-c180d7c6c56a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanBenefitObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward_13b2505f-d21f-4025-8a92-25f4825d6bfb" xlink:to="loc_us-gaap_DefinedBenefitPlanBenefitObligation_8896290c-eae7-4722-be24-c180d7c6c56a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanServiceCost_704bc2e2-a78a-415d-bf71-30e213e1bb22" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanServiceCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward_13b2505f-d21f-4025-8a92-25f4825d6bfb" xlink:to="loc_us-gaap_DefinedBenefitPlanServiceCost_704bc2e2-a78a-415d-bf71-30e213e1bb22" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanInterestCost_c7d52f47-dbdc-465f-9ae3-87d9c954e718" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanInterestCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward_13b2505f-d21f-4025-8a92-25f4825d6bfb" xlink:to="loc_us-gaap_DefinedBenefitPlanInterestCost_c7d52f47-dbdc-465f-9ae3-87d9c954e718" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanActuarialGainLoss_4ec16f85-8695-447e-ac8d-07b9d1049ecb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanActuarialGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward_13b2505f-d21f-4025-8a92-25f4825d6bfb" xlink:to="loc_us-gaap_DefinedBenefitPlanActuarialGainLoss_4ec16f85-8695-447e-ac8d-07b9d1049ecb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesBenefitObligation_015089b4-ec2d-4170-a35d-da1b37900abf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesBenefitObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward_13b2505f-d21f-4025-8a92-25f4825d6bfb" xlink:to="loc_us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesBenefitObligation_015089b4-ec2d-4170-a35d-da1b37900abf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanBenefitObligationBenefitsPaid_9a09d61e-6f6c-48e7-8a68-cdee03d6a543" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanBenefitObligationBenefitsPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward_13b2505f-d21f-4025-8a92-25f4825d6bfb" xlink:to="loc_us-gaap_DefinedBenefitPlanBenefitObligationBenefitsPaid_9a09d61e-6f6c-48e7-8a68-cdee03d6a543" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanBenefitObligation_ba500e5b-5254-4d32-8a16-b2bbc2fb70d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanBenefitObligation"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward_d4c29482-7c31-4622-97d8-c2670fc981a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_1d8c77d1-650e-438c-bf90-e560cb60b403" xlink:to="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward_d4c29482-7c31-4622-97d8-c2670fc981a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_9811cab2-4d63-4b24-ab4b-3b9bfc0ca036" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward_d4c29482-7c31-4622-97d8-c2670fc981a1" xlink:to="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_9811cab2-4d63-4b24-ab4b-3b9bfc0ca036" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets_b8ab87d1-44f4-4132-96bc-25a82d4b8047" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward_d4c29482-7c31-4622-97d8-c2670fc981a1" xlink:to="loc_us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets_b8ab87d1-44f4-4132-96bc-25a82d4b8047" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanContributionsByEmployer_cadb504b-d0d4-48ba-ac47-bb107690e3ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanContributionsByEmployer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward_d4c29482-7c31-4622-97d8-c2670fc981a1" xlink:to="loc_us-gaap_DefinedBenefitPlanContributionsByEmployer_cadb504b-d0d4-48ba-ac47-bb107690e3ab" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanSettlementsPlanAssets_c4750535-b068-4fbd-aa03-9224655cd6d0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanSettlementsPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward_d4c29482-7c31-4622-97d8-c2670fc981a1" xlink:to="loc_us-gaap_DefinedBenefitPlanSettlementsPlanAssets_c4750535-b068-4fbd-aa03-9224655cd6d0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPlanAssetsForeignCurrencyTranslationGainLoss_60201506-3adc-41d2-82bd-86b57c15bf2c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanPlanAssetsForeignCurrencyTranslationGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward_d4c29482-7c31-4622-97d8-c2670fc981a1" xlink:to="loc_us-gaap_DefinedBenefitPlanPlanAssetsForeignCurrencyTranslationGainLoss_60201506-3adc-41d2-82bd-86b57c15bf2c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPlanAssetsBenefitsPaid_56c809aa-306b-4470-8050-4ff69da8bf94" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanPlanAssetsBenefitsPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward_d4c29482-7c31-4622-97d8-c2670fc981a1" xlink:to="loc_us-gaap_DefinedBenefitPlanPlanAssetsBenefitsPaid_56c809aa-306b-4470-8050-4ff69da8bf94" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_bc805fd1-b8bc-4c7d-a4fa-6e1581b4e325" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlanAbstract_f3806547-6087-4a78-8fa0-3cf4e0ff3be2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanFundedStatusOfPlanAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_1d8c77d1-650e-438c-bf90-e560cb60b403" xlink:to="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlanAbstract_f3806547-6087-4a78-8fa0-3cf4e0ff3be2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlan_5866057b-8bdb-40df-b837-2310f0a15920" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanFundedStatusOfPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlanAbstract_f3806547-6087-4a78-8fa0-3cf4e0ff3be2" xlink:to="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlan_5866057b-8bdb-40df-b837-2310f0a15920" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanCurtailments_7f21c13d-2481-4e88-ad5f-e0daca099d00" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanCurtailments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_1d8c77d1-650e-438c-bf90-e560cb60b403" xlink:to="loc_us-gaap_DefinedBenefitPlanCurtailments_7f21c13d-2481-4e88-ad5f-e0daca099d00" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanBenefitObligationPaymentForSettlement_60ce4657-caaf-4612-b497-a9c62d24173b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanBenefitObligationPaymentForSettlement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_1d8c77d1-650e-438c-bf90-e560cb60b403" xlink:to="loc_us-gaap_DefinedBenefitPlanBenefitObligationPaymentForSettlement_60ce4657-caaf-4612-b497-a9c62d24173b" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/BenefitPlansAmountsRecordedinConsolidatedBalanceSheetsDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#BenefitPlansAmountsRecordedinConsolidatedBalanceSheetsDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/BenefitPlansAmountsRecordedinConsolidatedBalanceSheetsDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_28d3b46f-08af-4316-b2c6-a3895c4d684a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_e0a55fd9-5854-425f-b5de-ed8cab5cb8cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_28d3b46f-08af-4316-b2c6-a3895c4d684a" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_e0a55fd9-5854-425f-b5de-ed8cab5cb8cf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_0ac3e0d5-6b22-4ce6-9e13-eb2bba676e9a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_e0a55fd9-5854-425f-b5de-ed8cab5cb8cf" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_0ac3e0d5-6b22-4ce6-9e13-eb2bba676e9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_0ac3e0d5-6b22-4ce6-9e13-eb2bba676e9a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_0ac3e0d5-6b22-4ce6-9e13-eb2bba676e9a" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_0ac3e0d5-6b22-4ce6-9e13-eb2bba676e9a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_a1ed56e9-fbf3-4e9c-921f-a46bd9cdb692" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_0ac3e0d5-6b22-4ce6-9e13-eb2bba676e9a" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_a1ed56e9-fbf3-4e9c-921f-a46bd9cdb692" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_b0a830e0-13a9-4ef9-9e66-f732e5dbc671" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_a1ed56e9-fbf3-4e9c-921f-a46bd9cdb692" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_b0a830e0-13a9-4ef9-9e66-f732e5dbc671" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_0be8d5aa-0957-4cca-b26d-a7804d18180c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_a1ed56e9-fbf3-4e9c-921f-a46bd9cdb692" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_0be8d5aa-0957-4cca-b26d-a7804d18180c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities_116c53ff-e5d3-42d1-a1ea-ea4bce8c9fc0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_28d3b46f-08af-4316-b2c6-a3895c4d684a" xlink:to="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities_116c53ff-e5d3-42d1-a1ea-ea4bce8c9fc0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent_8d2a861a-1820-4bcb-9377-b3d6ffef3fad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_28d3b46f-08af-4316-b2c6-a3895c4d684a" xlink:to="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent_8d2a861a-1820-4bcb-9377-b3d6ffef3fad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesCurrentAndNoncurrent_9d9d9356-a180-43ff-9838-99ccff8509ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_28d3b46f-08af-4316-b2c6-a3895c4d684a" xlink:to="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesCurrentAndNoncurrent_9d9d9356-a180-43ff-9838-99ccff8509ad" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/BenefitPlansNarrativeDetails" xlink:type="simple" xlink:href="pnr-20251231.xsd#BenefitPlansNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/BenefitPlansNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_226aa230-d4a1-4ca7-b4a7-1a7a801bd404" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_020d2f93-63bf-48c7-8153-1db71f7d1b02" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_226aa230-d4a1-4ca7-b4a7-1a7a801bd404" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_020d2f93-63bf-48c7-8153-1db71f7d1b02" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_2f3fb22c-eb12-4158-a8e2-fac911bd864b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_020d2f93-63bf-48c7-8153-1db71f7d1b02" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_2f3fb22c-eb12-4158-a8e2-fac911bd864b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_2f3fb22c-eb12-4158-a8e2-fac911bd864b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_2f3fb22c-eb12-4158-a8e2-fac911bd864b" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_2f3fb22c-eb12-4158-a8e2-fac911bd864b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_d0c14bac-a30d-40b8-adbd-a8233f79ba1f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_2f3fb22c-eb12-4158-a8e2-fac911bd864b" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_d0c14bac-a30d-40b8-adbd-a8233f79ba1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_b0ec094c-86df-452c-8fcf-6ad3916f46ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_d0c14bac-a30d-40b8-adbd-a8233f79ba1f" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_b0ec094c-86df-452c-8fcf-6ad3916f46ac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DefinedContributionPensionandOtherPostretirementPlansAxis_8513ee41-5067-4c43-8fa8-2c8bfc2a16e0" xlink:href="pnr-20251231.xsd#pnr_DefinedContributionPensionandOtherPostretirementPlansAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_020d2f93-63bf-48c7-8153-1db71f7d1b02" xlink:to="loc_pnr_DefinedContributionPensionandOtherPostretirementPlansAxis_8513ee41-5067-4c43-8fa8-2c8bfc2a16e0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DefinedContributionPensionAndOtherPostretirementPlansDomain_8513ee41-5067-4c43-8fa8-2c8bfc2a16e0_default" xlink:href="pnr-20251231.xsd#pnr_DefinedContributionPensionAndOtherPostretirementPlansDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_pnr_DefinedContributionPensionandOtherPostretirementPlansAxis_8513ee41-5067-4c43-8fa8-2c8bfc2a16e0" xlink:to="loc_pnr_DefinedContributionPensionAndOtherPostretirementPlansDomain_8513ee41-5067-4c43-8fa8-2c8bfc2a16e0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DefinedContributionPensionAndOtherPostretirementPlansDomain_f89250d9-7dd3-45a7-a3bb-7245a362efbb" xlink:href="pnr-20251231.xsd#pnr_DefinedContributionPensionAndOtherPostretirementPlansDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_pnr_DefinedContributionPensionandOtherPostretirementPlansAxis_8513ee41-5067-4c43-8fa8-2c8bfc2a16e0" xlink:to="loc_pnr_DefinedContributionPensionAndOtherPostretirementPlansDomain_f89250d9-7dd3-45a7-a3bb-7245a362efbb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_A401KPlanLegacyGroupOneMember_c6623f36-72e0-46f8-8fd2-30180df85ecc" xlink:href="pnr-20251231.xsd#pnr_A401KPlanLegacyGroupOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_DefinedContributionPensionAndOtherPostretirementPlansDomain_f89250d9-7dd3-45a7-a3bb-7245a362efbb" xlink:to="loc_pnr_A401KPlanLegacyGroupOneMember_c6623f36-72e0-46f8-8fd2-30180df85ecc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_A401KPlanLegacyGroupTwoMember_ac25c1a0-e5f4-4d78-97ab-7fcc7acc2b60" xlink:href="pnr-20251231.xsd#pnr_A401KPlanLegacyGroupTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_DefinedContributionPensionAndOtherPostretirementPlansDomain_f89250d9-7dd3-45a7-a3bb-7245a362efbb" xlink:to="loc_pnr_A401KPlanLegacyGroupTwoMember_ac25c1a0-e5f4-4d78-97ab-7fcc7acc2b60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_Flow401KPlanMember_47bdf84f-a1c6-45ae-af7a-6c0c94eaf243" xlink:href="pnr-20251231.xsd#pnr_Flow401KPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_DefinedContributionPensionAndOtherPostretirementPlansDomain_f89250d9-7dd3-45a7-a3bb-7245a362efbb" xlink:to="loc_pnr_Flow401KPlanMember_47bdf84f-a1c6-45ae-af7a-6c0c94eaf243" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation_b692bdbd-6ba3-4bb9-a5bf-bccafbb8acec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_226aa230-d4a1-4ca7-b4a7-1a7a801bd404" xlink:to="loc_us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation_b692bdbd-6ba3-4bb9-a5bf-bccafbb8acec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_HistoricalRateOfReturnOnPlanAssets_b2d4c549-c7b5-4a7f-bb21-2cf03102071e" xlink:href="pnr-20251231.xsd#pnr_HistoricalRateOfReturnOnPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_226aa230-d4a1-4ca7-b4a7-1a7a801bd404" xlink:to="loc_pnr_HistoricalRateOfReturnOnPlanAssets_b2d4c549-c7b5-4a7f-bb21-2cf03102071e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanContributionsByEmployer_cb61a2f9-809f-4092-98c9-05dd1eeeab32" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanContributionsByEmployer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_226aa230-d4a1-4ca7-b4a7-1a7a801bd404" xlink:to="loc_us-gaap_DefinedBenefitPlanContributionsByEmployer_cb61a2f9-809f-4092-98c9-05dd1eeeab32" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear_e4d01c3e-16b1-4cba-8d78-9ae8a947c267" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_226aa230-d4a1-4ca7-b4a7-1a7a801bd404" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear_e4d01c3e-16b1-4cba-8d78-9ae8a947c267" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent_aa97c54b-6d8e-4048-9c68-07fed9d886a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_226aa230-d4a1-4ca7-b4a7-1a7a801bd404" xlink:to="loc_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent_aa97c54b-6d8e-4048-9c68-07fed9d886a7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent_68bf3199-d40f-41d4-be52-0e92482581e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_226aa230-d4a1-4ca7-b4a7-1a7a801bd404" xlink:to="loc_us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent_68bf3199-d40f-41d4-be52-0e92482581e4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeBenefitsAndShareBasedCompensation_cb0ed2cf-2c6f-4d8b-a580-6dea4b5481e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeBenefitsAndShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_226aa230-d4a1-4ca7-b4a7-1a7a801bd404" xlink:to="loc_us-gaap_EmployeeBenefitsAndShareBasedCompensation_cb0ed2cf-2c6f-4d8b-a580-6dea4b5481e2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherDeferredCompensationArrangementsLiabilityCurrent_49716990-2b64-4b14-ba80-c2eb65d3ea6f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherDeferredCompensationArrangementsLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_226aa230-d4a1-4ca7-b4a7-1a7a801bd404" xlink:to="loc_us-gaap_OtherDeferredCompensationArrangementsLiabilityCurrent_49716990-2b64-4b14-ba80-c2eb65d3ea6f" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/BenefitPlansScheduleofAssumptionsDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#BenefitPlansScheduleofAssumptionsDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/BenefitPlansScheduleofAssumptionsDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_c89077e0-01df-4f29-8059-3de29c995d3d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_d46ea500-af7d-45d8-a59e-e68b50f1100c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_c89077e0-01df-4f29-8059-3de29c995d3d" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_d46ea500-af7d-45d8-a59e-e68b50f1100c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_52acb5e6-13e8-49e6-ad4c-ec025a511d75" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_d46ea500-af7d-45d8-a59e-e68b50f1100c" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_52acb5e6-13e8-49e6-ad4c-ec025a511d75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_52acb5e6-13e8-49e6-ad4c-ec025a511d75_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_52acb5e6-13e8-49e6-ad4c-ec025a511d75" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_52acb5e6-13e8-49e6-ad4c-ec025a511d75_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_f9aa70b0-d77f-4601-96d3-ca7e6d08cf50" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_52acb5e6-13e8-49e6-ad4c-ec025a511d75" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_f9aa70b0-d77f-4601-96d3-ca7e6d08cf50" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_a545cbdb-0e0b-4598-9bb5-8c1c5cb1c634" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_f9aa70b0-d77f-4601-96d3-ca7e6d08cf50" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_a545cbdb-0e0b-4598-9bb5-8c1c5cb1c634" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_a61879dc-adde-4188-9b8b-acd22958f60c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_f9aa70b0-d77f-4601-96d3-ca7e6d08cf50" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_a61879dc-adde-4188-9b8b-acd22958f60c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingBenefitObligationAbstract_c065c1fb-5ab5-4079-8d72-9fcc336abda9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingBenefitObligationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_c89077e0-01df-4f29-8059-3de29c995d3d" xlink:to="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingBenefitObligationAbstract_c065c1fb-5ab5-4079-8d72-9fcc336abda9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate_133274b0-94de-4992-bc87-7142e31f2743" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingBenefitObligationAbstract_c065c1fb-5ab5-4079-8d72-9fcc336abda9" xlink:to="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate_133274b0-94de-4992-bc87-7142e31f2743" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease_cff17487-63d2-4a94-bde1-8f9c1bfebe77" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingBenefitObligationAbstract_c065c1fb-5ab5-4079-8d72-9fcc336abda9" xlink:to="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease_cff17487-63d2-4a94-bde1-8f9c1bfebe77" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract_4e7ca364-eef8-476a-920e-d4e51581c144" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_c89077e0-01df-4f29-8059-3de29c995d3d" xlink:to="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract_4e7ca364-eef8-476a-920e-d4e51581c144" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate_42801bd6-c5d2-4e67-9095-5f1b36741bd9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract_4e7ca364-eef8-476a-920e-d4e51581c144" xlink:to="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate_42801bd6-c5d2-4e67-9095-5f1b36741bd9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets_b436efcb-0a48-4b0f-a886-93839f7cf683" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract_4e7ca364-eef8-476a-920e-d4e51581c144" xlink:to="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets_b436efcb-0a48-4b0f-a886-93839f7cf683" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease_4adea7c3-9243-468a-878f-95bd07720046" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract_4e7ca364-eef8-476a-920e-d4e51581c144" xlink:to="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease_4adea7c3-9243-468a-878f-95bd07720046" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/BenefitPlansActualOverallAssetAllocationforUSAndNonUSPlansasComparedtoInvestmentPolicyGoalsDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#BenefitPlansActualOverallAssetAllocationforUSAndNonUSPlansasComparedtoInvestmentPolicyGoalsDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/BenefitPlansActualOverallAssetAllocationforUSAndNonUSPlansasComparedtoInvestmentPolicyGoalsDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_3c52c151-bd96-4a15-9adb-15d567ca3739" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_79708977-1fcf-4e59-b2b7-440822ff6844" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_3c52c151-bd96-4a15-9adb-15d567ca3739" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_79708977-1fcf-4e59-b2b7-440822ff6844" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_00167bc0-831d-4ff3-8e4f-b70f4d20e41c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_79708977-1fcf-4e59-b2b7-440822ff6844" xlink:to="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_00167bc0-831d-4ff3-8e4f-b70f4d20e41c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_00167bc0-831d-4ff3-8e4f-b70f4d20e41c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_00167bc0-831d-4ff3-8e4f-b70f4d20e41c" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_00167bc0-831d-4ff3-8e4f-b70f4d20e41c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_1d3af545-11d9-4bf8-94d7-821beea9989c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_00167bc0-831d-4ff3-8e4f-b70f4d20e41c" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_1d3af545-11d9-4bf8-94d7-821beea9989c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedIncomeSecuritiesMember_83eab727-2568-4809-b661-f070b21aea06" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FixedIncomeSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_1d3af545-11d9-4bf8-94d7-821beea9989c" xlink:to="loc_us-gaap_FixedIncomeSecuritiesMember_83eab727-2568-4809-b661-f070b21aea06" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_OtherSecuritiesMember_46aaf730-6ed4-4430-9012-04b3596badc9" xlink:href="pnr-20251231.xsd#pnr_OtherSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_1d3af545-11d9-4bf8-94d7-821beea9989c" xlink:to="loc_pnr_OtherSecuritiesMember_46aaf730-6ed4-4430-9012-04b3596badc9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanCashAndCashEquivalentsMember_f3484020-f3a2-4e16-a399-498134554060" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_1d3af545-11d9-4bf8-94d7-821beea9989c" xlink:to="loc_us-gaap_DefinedBenefitPlanCashAndCashEquivalentsMember_f3484020-f3a2-4e16-a399-498134554060" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsAbstract_88f39aea-4557-403a-9a6b-576d8e255a14" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_3c52c151-bd96-4a15-9adb-15d567ca3739" xlink:to="loc_us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsAbstract_88f39aea-4557-403a-9a6b-576d8e255a14" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations_9949481d-99ef-407d-8ac1-e942d0e7bd32" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsAbstract_88f39aea-4557-403a-9a6b-576d8e255a14" xlink:to="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations_9949481d-99ef-407d-8ac1-e942d0e7bd32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssetsTargetAllocationsAbstract_6f376d81-455a-42db-9bb9-debf9a59deaf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAssetsTargetAllocationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_3c52c151-bd96-4a15-9adb-15d567ca3739" xlink:to="loc_us-gaap_DefinedBenefitPlanAssetsTargetAllocationsAbstract_6f376d81-455a-42db-9bb9-debf9a59deaf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage_f47710cc-16f8-4fda-9bf8-8caef8b58498" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanAssetsTargetAllocationsAbstract_6f376d81-455a-42db-9bb9-debf9a59deaf" xlink:to="loc_us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage_f47710cc-16f8-4fda-9bf8-8caef8b58498" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/BenefitPlansPlanAssetsUsingFairValueMethodologiesDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#BenefitPlansPlanAssetsUsingFairValueMethodologiesDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/BenefitPlansPlanAssetsUsingFairValueMethodologiesDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_8f3e049b-5dd2-44b7-a3bc-19700671e9e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_ad818cb0-cafd-44cd-af6a-eae23ea711b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_8f3e049b-5dd2-44b7-a3bc-19700671e9e0" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_ad818cb0-cafd-44cd-af6a-eae23ea711b6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_21481e6f-3ba1-43c5-8a3c-0eb52fdd0c69" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_ad818cb0-cafd-44cd-af6a-eae23ea711b6" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_21481e6f-3ba1-43c5-8a3c-0eb52fdd0c69" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_21481e6f-3ba1-43c5-8a3c-0eb52fdd0c69_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_21481e6f-3ba1-43c5-8a3c-0eb52fdd0c69" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_21481e6f-3ba1-43c5-8a3c-0eb52fdd0c69_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_21acf473-ef6b-48bb-9b15-694e349c1303" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_21481e6f-3ba1-43c5-8a3c-0eb52fdd0c69" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_21acf473-ef6b-48bb-9b15-694e349c1303" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel12And3Member_ece743ea-7206-4667-b0f3-28d8fb9f4934" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel12And3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_21acf473-ef6b-48bb-9b15-694e349c1303" xlink:to="loc_us-gaap_FairValueInputsLevel12And3Member_ece743ea-7206-4667-b0f3-28d8fb9f4934" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_2a4594d7-d46b-4113-8c77-0dd78f941ff5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInputsLevel12And3Member_ece743ea-7206-4667-b0f3-28d8fb9f4934" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_2a4594d7-d46b-4113-8c77-0dd78f941ff5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_0f6bf153-558f-4fdf-8800-d946446bbf4e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInputsLevel12And3Member_ece743ea-7206-4667-b0f3-28d8fb9f4934" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_0f6bf153-558f-4fdf-8800-d946446bbf4e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_c5ca8b15-56b9-4c8b-8382-ff7c33f2439f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInputsLevel12And3Member_ece743ea-7206-4667-b0f3-28d8fb9f4934" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_c5ca8b15-56b9-4c8b-8382-ff7c33f2439f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember_c8f847f8-f925-434f-bf21-1209c0ee5ff1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_21acf473-ef6b-48bb-9b15-694e349c1303" xlink:to="loc_us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember_c8f847f8-f925-434f-bf21-1209c0ee5ff1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_b0f290a8-a5b1-4164-8cee-ffe1d0635256" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_ad818cb0-cafd-44cd-af6a-eae23ea711b6" xlink:to="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_b0f290a8-a5b1-4164-8cee-ffe1d0635256" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_b0f290a8-a5b1-4164-8cee-ffe1d0635256_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_b0f290a8-a5b1-4164-8cee-ffe1d0635256" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_b0f290a8-a5b1-4164-8cee-ffe1d0635256_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_6001ded5-cfad-4e61-a0ca-fa4570150869" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_b0f290a8-a5b1-4164-8cee-ffe1d0635256" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_6001ded5-cfad-4e61-a0ca-fa4570150869" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanCashAndCashEquivalentsMember_aa54ed6a-5af9-4ba2-a918-9a81563e707a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_6001ded5-cfad-4e61-a0ca-fa4570150869" xlink:to="loc_us-gaap_DefinedBenefitPlanCashAndCashEquivalentsMember_aa54ed6a-5af9-4ba2-a918-9a81563e707a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherInvestmentsMember_156d539b-1d27-45dd-a9d2-41dd6ba217a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_6001ded5-cfad-4e61-a0ca-fa4570150869" xlink:to="loc_us-gaap_OtherInvestmentsMember_156d539b-1d27-45dd-a9d2-41dd6ba217a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_e556d2de-0e42-4154-b5bb-3880bca61c96" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_8f3e049b-5dd2-44b7-a3bc-19700671e9e0" xlink:to="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_e556d2de-0e42-4154-b5bb-3880bca61c96" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward_2234ac4b-f1fe-4f6f-b7b6-08cbe8042886" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_8f3e049b-5dd2-44b7-a3bc-19700671e9e0" xlink:to="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward_2234ac4b-f1fe-4f6f-b7b6-08cbe8042886" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_265e0b12-db7e-4310-9085-9bfdb3503460" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DefinedBenefitPlanPlanAssetsLevel3ReconciliationIncreaseDecreaseForActualReturnLossOnPlanAssets_264eb963-7441-4d7b-a7a1-24cbbc627914" xlink:href="pnr-20251231.xsd#pnr_DefinedBenefitPlanPlanAssetsLevel3ReconciliationIncreaseDecreaseForActualReturnLossOnPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward_2234ac4b-f1fe-4f6f-b7b6-08cbe8042886" xlink:to="loc_pnr_DefinedBenefitPlanPlanAssetsLevel3ReconciliationIncreaseDecreaseForActualReturnLossOnPlanAssets_264eb963-7441-4d7b-a7a1-24cbbc627914" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DefinedBenefitPlanPlanAssetsLevel3ReconciliationCompanyContributions_3780eb04-a3bd-4bda-85b1-92759346369e" xlink:href="pnr-20251231.xsd#pnr_DefinedBenefitPlanPlanAssetsLevel3ReconciliationCompanyContributions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward_2234ac4b-f1fe-4f6f-b7b6-08cbe8042886" xlink:to="loc_pnr_DefinedBenefitPlanPlanAssetsLevel3ReconciliationCompanyContributions_3780eb04-a3bd-4bda-85b1-92759346369e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DefinedBenefitPlanLevel3ReconciliationIncreaseForBenefitsReceived_46e88e61-ed16-4412-8db3-eea91242198d" xlink:href="pnr-20251231.xsd#pnr_DefinedBenefitPlanLevel3ReconciliationIncreaseForBenefitsReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward_2234ac4b-f1fe-4f6f-b7b6-08cbe8042886" xlink:to="loc_pnr_DefinedBenefitPlanLevel3ReconciliationIncreaseForBenefitsReceived_46e88e61-ed16-4412-8db3-eea91242198d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPlanAssetsLevel3ReconciliationDecreaseForSettlement_09baada4-68a8-4b42-ba1e-4ec38019a910" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanPlanAssetsLevel3ReconciliationDecreaseForSettlement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward_2234ac4b-f1fe-4f6f-b7b6-08cbe8042886" xlink:to="loc_us-gaap_DefinedBenefitPlanPlanAssetsLevel3ReconciliationDecreaseForSettlement_09baada4-68a8-4b42-ba1e-4ec38019a910" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DefinedBenefitPlanPlanAssetsLevel3ReconciliationForeignCurrencyTranslation_584d0055-19cc-413b-92c6-1c850eca15a6" xlink:href="pnr-20251231.xsd#pnr_DefinedBenefitPlanPlanAssetsLevel3ReconciliationForeignCurrencyTranslation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward_2234ac4b-f1fe-4f6f-b7b6-08cbe8042886" xlink:to="loc_pnr_DefinedBenefitPlanPlanAssetsLevel3ReconciliationForeignCurrencyTranslation_584d0055-19cc-413b-92c6-1c850eca15a6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_d8d7471a-15f4-489d-8fea-2936cb44d004" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/BenefitPlansEstimatedfuturebenefitpaymentsDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#BenefitPlansEstimatedfuturebenefitpaymentsDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/BenefitPlansEstimatedfuturebenefitpaymentsDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_85ba8efd-7269-4554-899e-0b6aee2b295e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_74f90da4-f884-43e1-bee3-2a7cd9e0721a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_85ba8efd-7269-4554-899e-0b6aee2b295e" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_74f90da4-f884-43e1-bee3-2a7cd9e0721a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_42c1b434-f4ef-4b7e-8499-edb8373aadea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_74f90da4-f884-43e1-bee3-2a7cd9e0721a" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_42c1b434-f4ef-4b7e-8499-edb8373aadea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_42c1b434-f4ef-4b7e-8499-edb8373aadea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_42c1b434-f4ef-4b7e-8499-edb8373aadea" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_42c1b434-f4ef-4b7e-8499-edb8373aadea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_a780be92-42b1-4e95-a404-110aff10e569" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_42c1b434-f4ef-4b7e-8499-edb8373aadea" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_a780be92-42b1-4e95-a404-110aff10e569" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_40a7191a-b36b-4e9b-8c1e-a58418a10c4c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_a780be92-42b1-4e95-a404-110aff10e569" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_40a7191a-b36b-4e9b-8c1e-a58418a10c4c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_04e3188c-719f-4b0c-a2ce-1678dce9ad52" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_a780be92-42b1-4e95-a404-110aff10e569" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_04e3188c-719f-4b0c-a2ce-1678dce9ad52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths_f10e8645-b370-482d-ae25-9aa1744d7921" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_85ba8efd-7269-4554-899e-0b6aee2b295e" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths_f10e8645-b370-482d-ae25-9aa1744d7921" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo_05191e5c-9e7d-4051-a4a1-b079d9d0acdc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_85ba8efd-7269-4554-899e-0b6aee2b295e" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo_05191e5c-9e7d-4051-a4a1-b079d9d0acdc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree_032939fe-ad0c-45bd-8a49-b2d1e13153e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_85ba8efd-7269-4554-899e-0b6aee2b295e" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree_032939fe-ad0c-45bd-8a49-b2d1e13153e6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour_c0892628-2cbc-4a02-a725-239b3b781db1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_85ba8efd-7269-4554-899e-0b6aee2b295e" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour_c0892628-2cbc-4a02-a725-239b3b781db1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive_018a2815-43eb-40a4-81a8-a91199edba57" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_85ba8efd-7269-4554-899e-0b6aee2b295e" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive_018a2815-43eb-40a4-81a8-a91199edba57" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DefinedBenefitPlanExpectedFutureBenefitPaymentsAfterYearFive_e1769ccd-e15d-4b03-9e47-fd6fe2943f1a" xlink:href="pnr-20251231.xsd#pnr_DefinedBenefitPlanExpectedFutureBenefitPaymentsAfterYearFive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_85ba8efd-7269-4554-899e-0b6aee2b295e" xlink:to="loc_pnr_DefinedBenefitPlanExpectedFutureBenefitPaymentsAfterYearFive_e1769ccd-e15d-4b03-9e47-fd6fe2943f1a" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/ShareholdersEquityDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#ShareholdersEquityDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/ShareholdersEquityDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pnr_StockholdersEquityNoteDisclosureLineItems_da410cbc-bc0a-4ab2-bb60-eaa918b80f2c" xlink:href="pnr-20251231.xsd#pnr_StockholdersEquityNoteDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_StockholdersEquityNoteDisclosureTable_703af9e9-4931-4344-882c-2f692d6fa38c" xlink:href="pnr-20251231.xsd#pnr_StockholdersEquityNoteDisclosureTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_da410cbc-bc0a-4ab2-bb60-eaa918b80f2c" xlink:to="loc_pnr_StockholdersEquityNoteDisclosureTable_703af9e9-4931-4344-882c-2f692d6fa38c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_e138229a-e556-40a1-9c40-4cde2168b855" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureTable_703af9e9-4931-4344-882c-2f692d6fa38c" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_e138229a-e556-40a1-9c40-4cde2168b855" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_e138229a-e556-40a1-9c40-4cde2168b855_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_e138229a-e556-40a1-9c40-4cde2168b855" xlink:to="loc_us-gaap_EquityComponentDomain_e138229a-e556-40a1-9c40-4cde2168b855_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_d234d046-a42a-4d35-849e-0b38fc26a0a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_e138229a-e556-40a1-9c40-4cde2168b855" xlink:to="loc_us-gaap_EquityComponentDomain_d234d046-a42a-4d35-849e-0b38fc26a0a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_1dba0d2f-d34b-4149-bb49-d9a8ce48a4db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_d234d046-a42a-4d35-849e-0b38fc26a0a7" xlink:to="loc_us-gaap_CommonStockMember_1dba0d2f-d34b-4149-bb49-d9a8ce48a4db" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_de3d718c-640f-4397-8c78-9b39ecb0e55c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_d234d046-a42a-4d35-849e-0b38fc26a0a7" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_de3d718c-640f-4397-8c78-9b39ecb0e55c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramAxis_2912a1ff-b284-4569-bae8-b1cfa3ce3350" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ShareRepurchaseProgramAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureTable_703af9e9-4931-4344-882c-2f692d6fa38c" xlink:to="loc_srt_ShareRepurchaseProgramAxis_2912a1ff-b284-4569-bae8-b1cfa3ce3350" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_2912a1ff-b284-4569-bae8-b1cfa3ce3350_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ShareRepurchaseProgramAxis_2912a1ff-b284-4569-bae8-b1cfa3ce3350" xlink:to="loc_srt_ShareRepurchaseProgramDomain_2912a1ff-b284-4569-bae8-b1cfa3ce3350_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_6f9afada-00bb-4e7c-b600-c75a4376c648" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ShareRepurchaseProgramAxis_2912a1ff-b284-4569-bae8-b1cfa3ce3350" xlink:to="loc_srt_ShareRepurchaseProgramDomain_6f9afada-00bb-4e7c-b600-c75a4376c648" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_December2020ShareRepurchaseProgramMember_3dfbeb5e-9eb2-453d-8bdf-fd7451b21e1a" xlink:href="pnr-20251231.xsd#pnr_December2020ShareRepurchaseProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_6f9afada-00bb-4e7c-b600-c75a4376c648" xlink:to="loc_pnr_December2020ShareRepurchaseProgramMember_3dfbeb5e-9eb2-453d-8bdf-fd7451b21e1a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_December2025ShareRepurchaseProgramMember_b2fa3576-72fc-4777-945f-869987955413" xlink:href="pnr-20251231.xsd#pnr_December2025ShareRepurchaseProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_6f9afada-00bb-4e7c-b600-c75a4376c648" xlink:to="loc_pnr_December2025ShareRepurchaseProgramMember_b2fa3576-72fc-4777-945f-869987955413" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019c57ed-3353-77a2-8c9e-07f4edb3d6a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureTable_703af9e9-4931-4344-882c-2f692d6fa38c" xlink:to="loc_us-gaap_AwardTypeAxis_019c57ed-3353-77a2-8c9e-07f4edb3d6a3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c57ed-3353-77a2-8c9e-07f4edb3d6a3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019c57ed-3353-77a2-8c9e-07f4edb3d6a3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c57ed-3353-77a2-8c9e-07f4edb3d6a3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c57ed-3353-7848-b747-92645cd81024" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019c57ed-3353-77a2-8c9e-07f4edb3d6a3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c57ed-3353-7848-b747-92645cd81024" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019c57ed-3353-7b1f-bd79-079776cd3d84" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c57ed-3353-7848-b747-92645cd81024" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019c57ed-3353-7b1f-bd79-079776cd3d84" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_7f0ee1ba-3b90-4ce6-8230-1f2c1c7dfd02" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_da410cbc-bc0a-4ab2-bb60-eaa918b80f2c" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_7f0ee1ba-3b90-4ce6-8230-1f2c1c7dfd02" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_65af0624-5820-47b3-881a-6913726fa5a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_da410cbc-bc0a-4ab2-bb60-eaa918b80f2c" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_65af0624-5820-47b3-881a-6913726fa5a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StockRepurchaseProgramAuthorizedAmount1_663b683f-a281-4058-9184-a2502350f541" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StockRepurchaseProgramAuthorizedAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_da410cbc-bc0a-4ab2-bb60-eaa918b80f2c" xlink:to="loc_srt_StockRepurchaseProgramAuthorizedAmount1_663b683f-a281-4058-9184-a2502350f541" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_d106c7d6-be35-45b3-bb14-b3f87f8c999e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_da410cbc-bc0a-4ab2-bb60-eaa918b80f2c" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_d106c7d6-be35-45b3-bb14-b3f87f8c999e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_cb8a0322-d210-4387-8058-cde024914f5a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_da410cbc-bc0a-4ab2-bb60-eaa918b80f2c" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_cb8a0322-d210-4387-8058-cde024914f5a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_6755b71f-b37c-4125-a069-bcb4749c7c66" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_da410cbc-bc0a-4ab2-bb60-eaa918b80f2c" xlink:to="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_6755b71f-b37c-4125-a069-bcb4749c7c66" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPayableAmountPerShare_620a06ca-1246-44b5-8c3d-2df7040a0281" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsPayableAmountPerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_da410cbc-bc0a-4ab2-bb60-eaa918b80f2c" xlink:to="loc_us-gaap_DividendsPayableAmountPerShare_620a06ca-1246-44b5-8c3d-2df7040a0281" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_IncreaseDecreasetoQuarterlyDividendRate_e0633767-4e94-420b-8c13-177ace3f7c3f" xlink:href="pnr-20251231.xsd#pnr_IncreaseDecreasetoQuarterlyDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_da410cbc-bc0a-4ab2-bb60-eaa918b80f2c" xlink:to="loc_pnr_IncreaseDecreasetoQuarterlyDividendRate_e0633767-4e94-420b-8c13-177ace3f7c3f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPayableCurrent_e67e3e18-e356-4563-8bd5-b2dd2e89cee6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_da410cbc-bc0a-4ab2-bb60-eaa918b80f2c" xlink:to="loc_us-gaap_DividendsPayableCurrent_e67e3e18-e356-4563-8bd5-b2dd2e89cee6" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareCashPaid_5050b138-5ea5-4c3b-ac39-7e934c2cdc68" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockDividendsPerShareCashPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_da410cbc-bc0a-4ab2-bb60-eaa918b80f2c" xlink:to="loc_us-gaap_CommonStockDividendsPerShareCashPaid_5050b138-5ea5-4c3b-ac39-7e934c2cdc68" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_019c57ed-3353-7874-9e87-777e2bd6dde1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_da410cbc-bc0a-4ab2-bb60-eaa918b80f2c" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_019c57ed-3353-7874-9e87-777e2bd6dde1" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/SharePlansSharebasedcompensationexpenseDetails" xlink:type="simple" xlink:href="pnr-20251231.xsd#SharePlansSharebasedcompensationexpenseDetails"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/SharePlansSharebasedcompensationexpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_ff811340-9172-4283-be73-5abb7f4b19be" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_a99207e6-7d72-4c72-9899-0e45378a99f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_ff811340-9172-4283-be73-5abb7f4b19be" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_a99207e6-7d72-4c72-9899-0e45378a99f0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_d3f5edaf-e806-4e40-a65e-e8ffb2ee0c43" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_a99207e6-7d72-4c72-9899-0e45378a99f0" xlink:to="loc_us-gaap_AwardTypeAxis_d3f5edaf-e806-4e40-a65e-e8ffb2ee0c43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d3f5edaf-e806-4e40-a65e-e8ffb2ee0c43_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_d3f5edaf-e806-4e40-a65e-e8ffb2ee0c43" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d3f5edaf-e806-4e40-a65e-e8ffb2ee0c43_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_730f4e87-f805-4a98-8657-76cd702cc531" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_d3f5edaf-e806-4e40-a65e-e8ffb2ee0c43" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_730f4e87-f805-4a98-8657-76cd702cc531" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockOptionMember_ed4932c3-c8ed-40c8-946a-2a92a3b691b2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_730f4e87-f805-4a98-8657-76cd702cc531" xlink:to="loc_us-gaap_StockOptionMember_ed4932c3-c8ed-40c8-946a-2a92a3b691b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_f0b77d7f-c243-4db8-88a4-93a803701315" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_730f4e87-f805-4a98-8657-76cd702cc531" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_f0b77d7f-c243-4db8-88a4-93a803701315" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_3a0b9e3d-3e01-4e0a-8155-962937cdb678" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_730f4e87-f805-4a98-8657-76cd702cc531" xlink:to="loc_us-gaap_PerformanceSharesMember_3a0b9e3d-3e01-4e0a-8155-962937cdb678" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_2a5b4018-9729-465b-a952-662067bfe703" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_ff811340-9172-4283-be73-5abb7f4b19be" xlink:to="loc_us-gaap_ShareBasedCompensation_2a5b4018-9729-465b-a952-662067bfe703" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/SharePlansNarrativeDetails" xlink:type="simple" xlink:href="pnr-20251231.xsd#SharePlansNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/SharePlansNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c6855-a27f-71da-9013-57e7b4830be7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019c6855-a27f-76fe-8294-0b047a35d95b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c6855-a27f-71da-9013-57e7b4830be7" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019c6855-a27f-76fe-8294-0b047a35d95b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019c6855-a27f-7df8-b6b8-ca54c0935fca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019c6855-a27f-76fe-8294-0b047a35d95b" xlink:to="loc_us-gaap_AwardTypeAxis_019c6855-a27f-7df8-b6b8-ca54c0935fca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c6855-a27f-7df8-b6b8-ca54c0935fca_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019c6855-a27f-7df8-b6b8-ca54c0935fca" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c6855-a27f-7df8-b6b8-ca54c0935fca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c6855-a27f-727d-911a-4e45cbec3415" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019c6855-a27f-7df8-b6b8-ca54c0935fca" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c6855-a27f-727d-911a-4e45cbec3415" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019c6855-a27f-7875-94f3-831b9e055fd5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c6855-a27f-727d-911a-4e45cbec3415" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019c6855-a27f-7875-94f3-831b9e055fd5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_RestrictedStockAndRestrictedStockUnitsRSUsMember_019c6855-a27f-70a3-87d6-77e52715c127" xlink:href="pnr-20251231.xsd#pnr_RestrictedStockAndRestrictedStockUnitsRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c6855-a27f-727d-911a-4e45cbec3415" xlink:to="loc_pnr_RestrictedStockAndRestrictedStockUnitsRSUsMember_019c6855-a27f-70a3-87d6-77e52715c127" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockAppreciationRightsSARSMember_019c6855-a27f-72fa-b064-d48519598a79" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockAppreciationRightsSARSMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c6855-a27f-727d-911a-4e45cbec3415" xlink:to="loc_us-gaap_StockAppreciationRightsSARSMember_019c6855-a27f-72fa-b064-d48519598a79" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019c6856-ef7d-7b7c-984d-cae0344ad2a5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c6855-a27f-727d-911a-4e45cbec3415" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019c6856-ef7d-7b7c-984d-cae0344ad2a5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019c6857-194e-7128-8322-90af87691d31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c6855-a27f-727d-911a-4e45cbec3415" xlink:to="loc_us-gaap_PerformanceSharesMember_019c6857-194e-7128-8322-90af87691d31" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_019c6857-9398-713d-b89d-a3eeee4ac17b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019c6855-a27f-76fe-8294-0b047a35d95b" xlink:to="loc_us-gaap_VestingAxis_019c6857-9398-713d-b89d-a3eeee4ac17b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019c6857-9398-713d-b89d-a3eeee4ac17b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_019c6857-9398-713d-b89d-a3eeee4ac17b" xlink:to="loc_us-gaap_VestingDomain_019c6857-9398-713d-b89d-a3eeee4ac17b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019c6857-9398-7a25-ace2-a01f06ebaf72" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_019c6857-9398-713d-b89d-a3eeee4ac17b" xlink:to="loc_us-gaap_VestingDomain_019c6857-9398-7a25-ace2-a01f06ebaf72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_019c6857-9398-7f53-bb56-1a9ec69e2251" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019c6857-9398-7a25-ace2-a01f06ebaf72" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_019c6857-9398-7f53-bb56-1a9ec69e2251" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_019c6857-9398-7b7e-bb92-74e9ab3459a8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019c6857-9398-7a25-ace2-a01f06ebaf72" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_019c6857-9398-7b7e-bb92-74e9ab3459a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_019c6857-9398-7ac8-a14e-81d7cdcd85fd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationAwardTrancheThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019c6857-9398-7a25-ace2-a01f06ebaf72" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_019c6857-9398-7ac8-a14e-81d7cdcd85fd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_019c6855-1bb9-78cb-a495-d44364a5db6b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c6855-a27f-71da-9013-57e7b4830be7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_019c6855-1bb9-78cb-a495-d44364a5db6b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_019c6855-1bb9-7a90-bdb6-d010b3737979" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c6855-a27f-71da-9013-57e7b4830be7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_019c6855-1bb9-7a90-bdb6-d010b3737979" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019c6855-a27f-70b8-b453-8e4b9323a56b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c6855-a27f-71da-9013-57e7b4830be7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019c6855-a27f-70b8-b453-8e4b9323a56b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpiryPeriodFromDateOfGrant_019c6855-a27f-7b38-ab34-9c60de93f5e0" xlink:href="pnr-20251231.xsd#pnr_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpiryPeriodFromDateOfGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c6855-a27f-71da-9013-57e7b4830be7" xlink:to="loc_pnr_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpiryPeriodFromDateOfGrant_019c6855-a27f-7b38-ab34-9c60de93f5e0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_019c6857-9398-799f-9c42-2d6cba662a5b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c6855-a27f-71da-9013-57e7b4830be7" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_019c6857-9398-799f-9c42-2d6cba662a5b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019c6856-9188-7a1b-9979-cec381470f45" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c6855-a27f-71da-9013-57e7b4830be7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019c6856-9188-7a1b-9979-cec381470f45" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_019c6856-9188-70b2-99b3-4f75958279f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c6855-a27f-71da-9013-57e7b4830be7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_019c6856-9188-70b2-99b3-4f75958279f8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019c6856-9188-77cb-9827-398968992b31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c6855-a27f-71da-9013-57e7b4830be7" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019c6856-9188-77cb-9827-398968992b31" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019c6856-9188-7a54-b423-9427203ff828" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c6855-a27f-71da-9013-57e7b4830be7" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019c6856-9188-7a54-b423-9427203ff828" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromStockOptionsExercised_019c6856-c7e3-71e0-a74d-6e2ff3bcea18" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c6855-a27f-71da-9013-57e7b4830be7" xlink:to="loc_us-gaap_ProceedsFromStockOptionsExercised_019c6856-c7e3-71e0-a74d-6e2ff3bcea18" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromExerciseOfStockOptions_019c6856-c7e3-7eb5-af71-bd0ef571ff81" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromExerciseOfStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c6855-a27f-71da-9013-57e7b4830be7" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromExerciseOfStockOptions_019c6856-c7e3-7eb5-af71-bd0ef571ff81" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_019c6856-ef7d-737f-9816-fd5581e323b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c6855-a27f-71da-9013-57e7b4830be7" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_019c6856-ef7d-737f-9816-fd5581e323b9" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_019c6856-ef7d-7c06-be76-228bfe179908" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c6855-a27f-71da-9013-57e7b4830be7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_019c6856-ef7d-7c06-be76-228bfe179908" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_019c6856-ef7d-709c-8154-c3c6b4121a8c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c6855-a27f-71da-9013-57e7b4830be7" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_019c6856-ef7d-709c-8154-c3c6b4121a8c" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/SharePlansRestrictedStockUnitsDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#SharePlansRestrictedStockUnitsDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/SharePlansRestrictedStockUnitsDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cbac556b-4df7-4e6f-aedb-8d1bab24ec5c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_5b747413-a026-494d-9117-1f4323cb9809" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cbac556b-4df7-4e6f-aedb-8d1bab24ec5c" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_5b747413-a026-494d-9117-1f4323cb9809" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_d1ee0e2e-34c8-41bc-b2fa-7479da9712a5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_5b747413-a026-494d-9117-1f4323cb9809" xlink:to="loc_us-gaap_AwardTypeAxis_d1ee0e2e-34c8-41bc-b2fa-7479da9712a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d1ee0e2e-34c8-41bc-b2fa-7479da9712a5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_d1ee0e2e-34c8-41bc-b2fa-7479da9712a5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d1ee0e2e-34c8-41bc-b2fa-7479da9712a5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a8b9d961-c218-4358-b90c-903e7bf74d4d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_d1ee0e2e-34c8-41bc-b2fa-7479da9712a5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a8b9d961-c218-4358-b90c-903e7bf74d4d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_35a2b09c-3913-4ca3-9a2b-39b5001ee7c3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a8b9d961-c218-4358-b90c-903e7bf74d4d" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_35a2b09c-3913-4ca3-9a2b-39b5001ee7c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_d5a9c076-a3c5-4d21-a181-184db602189b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cbac556b-4df7-4e6f-aedb-8d1bab24ec5c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_d5a9c076-a3c5-4d21-a181-184db602189b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_2c996fc5-08b1-4e6d-a708-9058994cc651" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_d5a9c076-a3c5-4d21-a181-184db602189b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_2c996fc5-08b1-4e6d-a708-9058994cc651" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_a88df5ce-a490-44a9-b365-c37e985c6ac6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_d5a9c076-a3c5-4d21-a181-184db602189b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_a88df5ce-a490-44a9-b365-c37e985c6ac6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_25a7a62f-01b7-4b11-ae02-383a61feb1fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_d5a9c076-a3c5-4d21-a181-184db602189b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_25a7a62f-01b7-4b11-ae02-383a61feb1fe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_811c8bb0-74f6-4849-9a90-7a5381b6e62f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_88a7ef0d-673d-4c7e-84d4-bdfba39c82e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cbac556b-4df7-4e6f-aedb-8d1bab24ec5c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_88a7ef0d-673d-4c7e-84d4-bdfba39c82e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_fc6e8a92-451b-45e8-9323-d26254c4f17b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_88a7ef0d-673d-4c7e-84d4-bdfba39c82e0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_fc6e8a92-451b-45e8-9323-d26254c4f17b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_4e39f6a7-db9a-4682-916a-977cfb61b6c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_88a7ef0d-673d-4c7e-84d4-bdfba39c82e0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_4e39f6a7-db9a-4682-916a-977cfb61b6c1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_7d34d63e-6b2b-4ee7-b1d8-2c92b8141266" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_88a7ef0d-673d-4c7e-84d4-bdfba39c82e0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_7d34d63e-6b2b-4ee7-b1d8-2c92b8141266" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_9e378d5c-185b-4af7-92ed-8716fe0b9a78" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/SharePlansPerformanceStockUnitsDetails" xlink:type="simple" xlink:href="pnr-20251231.xsd#SharePlansPerformanceStockUnitsDetails"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/SharePlansPerformanceStockUnitsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6367a401-646b-4169-8d45-ea622fe8e37c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_e76950ec-4b25-4b32-917e-ad4e7a5730c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6367a401-646b-4169-8d45-ea622fe8e37c" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_e76950ec-4b25-4b32-917e-ad4e7a5730c0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_759d5d2b-292f-41a6-83a2-99762ba015fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_e76950ec-4b25-4b32-917e-ad4e7a5730c0" xlink:to="loc_us-gaap_AwardTypeAxis_759d5d2b-292f-41a6-83a2-99762ba015fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_759d5d2b-292f-41a6-83a2-99762ba015fe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_759d5d2b-292f-41a6-83a2-99762ba015fe" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_759d5d2b-292f-41a6-83a2-99762ba015fe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_07925c3c-b27b-4604-b185-d193a8ff6b5e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_759d5d2b-292f-41a6-83a2-99762ba015fe" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_07925c3c-b27b-4604-b185-d193a8ff6b5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_488f28b3-6450-4c4c-9b15-24f6ea05c5db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_07925c3c-b27b-4604-b185-d193a8ff6b5e" xlink:to="loc_us-gaap_PerformanceSharesMember_488f28b3-6450-4c4c-9b15-24f6ea05c5db" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_5fad9d7d-bf07-4fc4-9713-b6760b1583b3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6367a401-646b-4169-8d45-ea622fe8e37c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_5fad9d7d-bf07-4fc4-9713-b6760b1583b3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_fbb2de75-0c18-4660-b9b9-4287a7d20dae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_5fad9d7d-bf07-4fc4-9713-b6760b1583b3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_fbb2de75-0c18-4660-b9b9-4287a7d20dae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_4c0e9d1e-e8da-456e-8653-065ff29b78db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_5fad9d7d-bf07-4fc4-9713-b6760b1583b3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_4c0e9d1e-e8da-456e-8653-065ff29b78db" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_caf53186-4c1f-4d93-94ec-4daa3164e880" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_5fad9d7d-bf07-4fc4-9713-b6760b1583b3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_caf53186-4c1f-4d93-94ec-4daa3164e880" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_b01174c7-434b-4d07-a61a-562ba750d622" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_83ddbeb1-37d1-4d96-9cf7-808bdc838d48" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6367a401-646b-4169-8d45-ea622fe8e37c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_83ddbeb1-37d1-4d96-9cf7-808bdc838d48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_9baf9b78-2474-4488-ac1f-763960c873fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_83ddbeb1-37d1-4d96-9cf7-808bdc838d48" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_9baf9b78-2474-4488-ac1f-763960c873fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_c4aae677-57fb-460f-8480-21a832c272d5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_83ddbeb1-37d1-4d96-9cf7-808bdc838d48" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_c4aae677-57fb-460f-8480-21a832c272d5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_21122002-8cf6-4cf9-ae24-581ec20c73a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_83ddbeb1-37d1-4d96-9cf7-808bdc838d48" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_21122002-8cf6-4cf9-ae24-581ec20c73a1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_3afe1c66-62e6-4d80-95e3-d9790540d119" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/SegmentInformationFinancialInformationByReportableSegmentDetail" xlink:type="simple" xlink:href="pnr-20251231.xsd#SegmentInformationFinancialInformationByReportableSegmentDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/SegmentInformationFinancialInformationByReportableSegmentDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_3a74d01c-b51e-4e2e-bcb9-d7d4e37d5d16" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_33a92743-872b-4a89-878d-314d616d7b95" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3a74d01c-b51e-4e2e-bcb9-d7d4e37d5d16" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_33a92743-872b-4a89-878d-314d616d7b95" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_1f5ee8fd-bbfd-40b3-92e5-af8c666b1726" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_33a92743-872b-4a89-878d-314d616d7b95" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_1f5ee8fd-bbfd-40b3-92e5-af8c666b1726" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_1f5ee8fd-bbfd-40b3-92e5-af8c666b1726_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_1f5ee8fd-bbfd-40b3-92e5-af8c666b1726" xlink:to="loc_us-gaap_SegmentDomain_1f5ee8fd-bbfd-40b3-92e5-af8c666b1726_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_493e5347-56ce-4df0-a0bb-9664c791d843" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_1f5ee8fd-bbfd-40b3-92e5-af8c666b1726" xlink:to="loc_us-gaap_SegmentDomain_493e5347-56ce-4df0-a0bb-9664c791d843" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_FlowMember_71eed1a0-984e-41fd-ad1a-c4fe1fb43466" xlink:href="pnr-20251231.xsd#pnr_FlowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_493e5347-56ce-4df0-a0bb-9664c791d843" xlink:to="loc_pnr_FlowMember_71eed1a0-984e-41fd-ad1a-c4fe1fb43466" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_WaterSolutionsMember_e214d31f-f77b-40c6-9923-fda12b60fa85" xlink:href="pnr-20251231.xsd#pnr_WaterSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_493e5347-56ce-4df0-a0bb-9664c791d843" xlink:to="loc_pnr_WaterSolutionsMember_e214d31f-f77b-40c6-9923-fda12b60fa85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_PoolMember_5e45e246-c131-44c8-b719-4b9ae4298594" xlink:href="pnr-20251231.xsd#pnr_PoolMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_493e5347-56ce-4df0-a0bb-9664c791d843" xlink:to="loc_pnr_PoolMember_5e45e246-c131-44c8-b719-4b9ae4298594" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_ceb1d347-0b81-40d3-a5ca-466230efcef8" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_33a92743-872b-4a89-878d-314d616d7b95" xlink:to="loc_srt_ConsolidationItemsAxis_ceb1d347-0b81-40d3-a5ca-466230efcef8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_ceb1d347-0b81-40d3-a5ca-466230efcef8_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_ceb1d347-0b81-40d3-a5ca-466230efcef8" xlink:to="loc_srt_ConsolidationItemsDomain_ceb1d347-0b81-40d3-a5ca-466230efcef8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_6a4f50c5-182e-4f57-a098-fbca5c4e8d69" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_ceb1d347-0b81-40d3-a5ca-466230efcef8" xlink:to="loc_srt_ConsolidationItemsDomain_6a4f50c5-182e-4f57-a098-fbca5c4e8d69" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_3282bc32-ca34-4246-aa64-8b312e9f49fc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_6a4f50c5-182e-4f57-a098-fbca5c4e8d69" xlink:to="loc_us-gaap_OperatingSegmentsMember_3282bc32-ca34-4246-aa64-8b312e9f49fc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_398a20e5-8060-49a9-a7d3-bdc2c35ff226" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_6a4f50c5-182e-4f57-a098-fbca5c4e8d69" xlink:to="loc_us-gaap_CorporateNonSegmentMember_398a20e5-8060-49a9-a7d3-bdc2c35ff226" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_c4e38530-f4b2-47ec-bb08-da75175f7eef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3a74d01c-b51e-4e2e-bcb9-d7d4e37d5d16" xlink:to="loc_us-gaap_Assets_c4e38530-f4b2-47ec-bb08-da75175f7eef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_d52d7392-d6cb-4f22-8603-8888d25ab2e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentExpenditureAdditionToLongLivedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3a74d01c-b51e-4e2e-bcb9-d7d4e37d5d16" xlink:to="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_d52d7392-d6cb-4f22-8603-8888d25ab2e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_866d1ecb-16cc-4eb0-b7d8-565e0552754c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3a74d01c-b51e-4e2e-bcb9-d7d4e37d5d16" xlink:to="loc_us-gaap_Depreciation_866d1ecb-16cc-4eb0-b7d8-565e0552754c" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/SegmentInformationReconciliationofIncomefromContinuingOperationsfromSegmentstoConsolidatedDetails" xlink:type="simple" xlink:href="pnr-20251231.xsd#SegmentInformationReconciliationofIncomefromContinuingOperationsfromSegmentstoConsolidatedDetails"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/SegmentInformationReconciliationofIncomefromContinuingOperationsfromSegmentstoConsolidatedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_22498127-3e45-4db7-bcce-355c9e323df6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTable_d7e561c2-1136-44b0-9a89-daaca41f525d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_22498127-3e45-4db7-bcce-355c9e323df6" xlink:to="loc_us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTable_d7e561c2-1136-44b0-9a89-daaca41f525d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_5ccf37c0-3081-4d43-a86c-6c1f5f0b3847" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTable_d7e561c2-1136-44b0-9a89-daaca41f525d" xlink:to="loc_srt_ConsolidationItemsAxis_5ccf37c0-3081-4d43-a86c-6c1f5f0b3847" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_5ccf37c0-3081-4d43-a86c-6c1f5f0b3847_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_5ccf37c0-3081-4d43-a86c-6c1f5f0b3847" xlink:to="loc_srt_ConsolidationItemsDomain_5ccf37c0-3081-4d43-a86c-6c1f5f0b3847_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_406a3bea-d2e4-4be5-9f05-7bf07f26d9cb" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_5ccf37c0-3081-4d43-a86c-6c1f5f0b3847" xlink:to="loc_srt_ConsolidationItemsDomain_406a3bea-d2e4-4be5-9f05-7bf07f26d9cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_74834b26-2e3a-47c1-afc6-6490a6b4dfdf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_406a3bea-d2e4-4be5-9f05-7bf07f26d9cb" xlink:to="loc_us-gaap_OperatingSegmentsMember_74834b26-2e3a-47c1-afc6-6490a6b4dfdf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_f0cead3d-e2a8-49b6-aa9e-b7b572b8c1cb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_406a3bea-d2e4-4be5-9f05-7bf07f26d9cb" xlink:to="loc_us-gaap_CorporateNonSegmentMember_f0cead3d-e2a8-49b6-aa9e-b7b572b8c1cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaterialReconcilingItemsMember_59d953d8-6ba7-4e41-b2a7-e9ba6b781f96" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MaterialReconcilingItemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_406a3bea-d2e4-4be5-9f05-7bf07f26d9cb" xlink:to="loc_us-gaap_MaterialReconcilingItemsMember_59d953d8-6ba7-4e41-b2a7-e9ba6b781f96" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_b5e55d3f-a6ca-4afb-9340-d0fe29e41810" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTable_d7e561c2-1136-44b0-9a89-daaca41f525d" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_b5e55d3f-a6ca-4afb-9340-d0fe29e41810" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_b5e55d3f-a6ca-4afb-9340-d0fe29e41810_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_b5e55d3f-a6ca-4afb-9340-d0fe29e41810" xlink:to="loc_us-gaap_SegmentDomain_b5e55d3f-a6ca-4afb-9340-d0fe29e41810_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_e7f6f79c-ff67-41da-bb07-8f2bf8b925f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_b5e55d3f-a6ca-4afb-9340-d0fe29e41810" xlink:to="loc_us-gaap_SegmentDomain_e7f6f79c-ff67-41da-bb07-8f2bf8b925f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_FlowMember_1bd70abb-810d-472e-b2d8-263e768530cb" xlink:href="pnr-20251231.xsd#pnr_FlowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_e7f6f79c-ff67-41da-bb07-8f2bf8b925f7" xlink:to="loc_pnr_FlowMember_1bd70abb-810d-472e-b2d8-263e768530cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_WaterSolutionsMember_d06a9991-607b-4732-bcd2-86a099639ca9" xlink:href="pnr-20251231.xsd#pnr_WaterSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_e7f6f79c-ff67-41da-bb07-8f2bf8b925f7" xlink:to="loc_pnr_WaterSolutionsMember_d06a9991-607b-4732-bcd2-86a099639ca9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_PoolMember_c9a2391f-b2c0-4b27-ba23-550d6c290db6" xlink:href="pnr-20251231.xsd#pnr_PoolMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_e7f6f79c-ff67-41da-bb07-8f2bf8b925f7" xlink:to="loc_pnr_PoolMember_c9a2391f-b2c0-4b27-ba23-550d6c290db6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_1edb9289-698a-4568-98c6-a6bda0c7a8e5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTable_d7e561c2-1136-44b0-9a89-daaca41f525d" xlink:to="loc_srt_MajorCustomersAxis_1edb9289-698a-4568-98c6-a6bda0c7a8e5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_1edb9289-698a-4568-98c6-a6bda0c7a8e5_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_1edb9289-698a-4568-98c6-a6bda0c7a8e5" xlink:to="loc_srt_NameOfMajorCustomerDomain_1edb9289-698a-4568-98c6-a6bda0c7a8e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_15da6d3a-0272-4c0e-b6b8-2a56091195c8" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_1edb9289-698a-4568-98c6-a6bda0c7a8e5" xlink:to="loc_srt_NameOfMajorCustomerDomain_15da6d3a-0272-4c0e-b6b8-2a56091195c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_CustomerOneMember_f330ad1e-3711-4719-982a-2f48af19e1ed" xlink:href="pnr-20251231.xsd#pnr_CustomerOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_15da6d3a-0272-4c0e-b6b8-2a56091195c8" xlink:to="loc_pnr_CustomerOneMember_f330ad1e-3711-4719-982a-2f48af19e1ed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_203d762b-03c1-4477-887f-02cedd7963e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTable_d7e561c2-1136-44b0-9a89-daaca41f525d" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_203d762b-03c1-4477-887f-02cedd7963e7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_203d762b-03c1-4477-887f-02cedd7963e7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_203d762b-03c1-4477-887f-02cedd7963e7" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_203d762b-03c1-4477-887f-02cedd7963e7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_1f2f7f66-88d2-4eca-b9b1-7ef5e6ac4bbf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_203d762b-03c1-4477-887f-02cedd7963e7" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_1f2f7f66-88d2-4eca-b9b1-7ef5e6ac4bbf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_17f425f7-af62-4df2-a864-3efc0c52435b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_1f2f7f66-88d2-4eca-b9b1-7ef5e6ac4bbf" xlink:to="loc_us-gaap_SalesRevenueNetMember_17f425f7-af62-4df2-a864-3efc0c52435b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_126117ff-8ce1-4d64-ad0d-f76330ec0484" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTable_d7e561c2-1136-44b0-9a89-daaca41f525d" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_126117ff-8ce1-4d64-ad0d-f76330ec0484" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_126117ff-8ce1-4d64-ad0d-f76330ec0484_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_126117ff-8ce1-4d64-ad0d-f76330ec0484" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_126117ff-8ce1-4d64-ad0d-f76330ec0484_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_67e82f8c-97d8-4df0-9a20-894e66f4c823" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_126117ff-8ce1-4d64-ad0d-f76330ec0484" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_67e82f8c-97d8-4df0-9a20-894e66f4c823" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_c24fe744-0676-40da-8597-5be95ba6630d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_67e82f8c-97d8-4df0-9a20-894e66f4c823" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_c24fe744-0676-40da-8597-5be95ba6630d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_dbbb44f1-5096-4156-aa6a-43711c580976" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_22498127-3e45-4db7-bcce-355c9e323df6" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_dbbb44f1-5096-4156-aa6a-43711c580976" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_cc16e50f-53a7-47e0-84c1-afb8c15b9df1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_22498127-3e45-4db7-bcce-355c9e323df6" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_cc16e50f-53a7-47e0-84c1-afb8c15b9df1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_5d436ada-90f0-4683-960c-3ab5d00ccd3e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_22498127-3e45-4db7-bcce-355c9e323df6" xlink:to="loc_us-gaap_OperatingExpenses_5d436ada-90f0-4683-960c-3ab5d00ccd3e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_0a6ddf69-1446-4b62-be87-a68fe3cddcda" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_22498127-3e45-4db7-bcce-355c9e323df6" xlink:to="loc_us-gaap_OperatingIncomeLoss_0a6ddf69-1446-4b62-be87-a68fe3cddcda" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_668dced1-4d6b-4341-8f8b-e931089d1385" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_22498127-3e45-4db7-bcce-355c9e323df6" xlink:to="loc_us-gaap_RestructuringCharges_668dced1-4d6b-4341-8f8b-e931089d1385" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TransformationCosts_51d33779-9324-4e24-a2b6-8ecd4430002e" xlink:href="pnr-20251231.xsd#pnr_TransformationCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_22498127-3e45-4db7-bcce-355c9e323df6" xlink:to="loc_pnr_TransformationCosts_51d33779-9324-4e24-a2b6-8ecd4430002e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations_2d3e2647-2b44-423f-ac65-2e2e630d9a99" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_22498127-3e45-4db7-bcce-355c9e323df6" xlink:to="loc_us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations_2d3e2647-2b44-423f-ac65-2e2e630d9a99" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetImpairmentCharges_07a9d59f-495e-425b-9d90-fd6a60d8dea8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_22498127-3e45-4db7-bcce-355c9e323df6" xlink:to="loc_us-gaap_AssetImpairmentCharges_07a9d59f-495e-425b-9d90-fd6a60d8dea8" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfBusiness_019c6863-814e-7647-a8d1-e539f8e898ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainLossOnSaleOfBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_22498127-3e45-4db7-bcce-355c9e323df6" xlink:to="loc_us-gaap_GainLossOnSaleOfBusiness_019c6863-814e-7647-a8d1-e539f8e898ef" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_Dealrelatedcostsandexpenses_a1944d25-d8c3-4e39-b113-8a0fad630742" xlink:href="pnr-20251231.xsd#pnr_Dealrelatedcostsandexpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_22498127-3e45-4db7-bcce-355c9e323df6" xlink:to="loc_pnr_Dealrelatedcostsandexpenses_a1944d25-d8c3-4e39-b113-8a0fad630742" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_LegalSettlementAndAccrualAdjustments_b674f702-5f26-4912-9391-56f75e783ae0" xlink:href="pnr-20251231.xsd#pnr_LegalSettlementAndAccrualAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_22498127-3e45-4db7-bcce-355c9e323df6" xlink:to="loc_pnr_LegalSettlementAndAccrualAdjustments_b674f702-5f26-4912-9391-56f75e783ae0" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_75346e72-2649-475a-acc7-d6a321ebd08a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_22498127-3e45-4db7-bcce-355c9e323df6" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_75346e72-2649-475a-acc7-d6a321ebd08a" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRevenueExpenseNet_7a46e623-3fc0-4390-b4ff-8d38348d1213" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRevenueExpenseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_22498127-3e45-4db7-bcce-355c9e323df6" xlink:to="loc_us-gaap_InterestRevenueExpenseNet_7a46e623-3fc0-4390-b4ff-8d38348d1213" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherExpenses_39c8a933-98dd-4d64-97a5-0c8d9179c19a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_22498127-3e45-4db7-bcce-355c9e323df6" xlink:to="loc_us-gaap_OtherExpenses_39c8a933-98dd-4d64-97a5-0c8d9179c19a" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_aef6e825-5a80-44d9-90c0-55d10867dc9e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_22498127-3e45-4db7-bcce-355c9e323df6" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_aef6e825-5a80-44d9-90c0-55d10867dc9e" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_e6ac6016-2b95-4906-86e0-6bbbde80286a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_22498127-3e45-4db7-bcce-355c9e323df6" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_e6ac6016-2b95-4906-86e0-6bbbde80286a" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-roles-2025.xsd#eedm"/>
  <link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsMiscellaneousNoncurrent" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherAssetsMiscellaneousNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract" xlink:to="loc_us-gaap_OtherAssetsMiscellaneousNoncurrent" xlink:type="arc" order="101"/>
  </link:definitionLink>
</link:linkbase>
