Plumber License Requirements in Washington
License RequiredLast verified March 9, 2026
Agency And Exam
Issuing agency: Washington State Department of Labor & Industries
Official licensing agency website
Exam provider: PSI
Reciprocity And License Levels
License levels
Journey Level PlumberResidential SpecialtyResidential Service PlumberMedical Gas EndorsementDomestic Pump / Pump and IrrigationBackflow Specialty
Reciprocity states
ID
Notes
Washington requires certification through the State Plumber Certification Program to work in the plumbing trade. L&I describes journey level and specialty plumber categories including residential, residential service, medical gas, domestic pump/pump and irrigation, and backflow, and it states Washington reciprocates with Idaho for journey level plumbers while other out-of-state applicants are reviewed individually. Verified against Washington L&I plumbing certification pages on 2026-03-09.