How Do You Get a Plumbing License in Washington?

Yes.

Washington requires certification by the L&I Plumber Certification Program to work in the plumbing trade anywhere in the state, and it reaches the first day of work: even a brand-new helper works on a plumber trainee certificate, under direct supervision.

The program covers the whole ladder — trainee, journey level, the specialty certificates and their endorsements.

The licence a business needs is separate: since July 2021, L&I requires a Plumbing Contractor licence to advertise, offer to do work, submit a bid, or perform plumbing work.

The ladder starts at the plumber trainee certificate, which lets you work only under the direct supervision of a certified plumber.

Journey level (PL01) is the top general certification: our cross-state review as of September 2026 found Washington issues a statewide journeyman-level licence but no state master licence.

Alongside journey level sit the specialty certificates — Residential (PL02), Residential Service (PL04), Pump & Irrigation (PL03), Domestic Well (PL03A) and Backflow (PL30) — plus the Medical Gas piping installer endorsement (MG01) for journey level plumbers.

On the business side, only licensed plumbing contractors may employ certified plumbers on plumbing jobs, and a general contractor that wants to do plumbing work needs the plumbing contractor licence too, with a separate bond.

Our research did not confirm the plumbing contractor licence's fee, renewal cycle or designated-plumber replacement deadline; confirm those with L&I.

Trainee: at least 16 years old, a $60 certificate valid 12 months, work under the direct supervision of a certified plumber, 8 hours of approved continuing education yearly to renew, and supervised hours reported yearly on notarized affidavits of experience.

Hours from out-of-state employers or out-of-state apprenticeship programs do not count.

Journey level (PL01) requires at least 8,000 hours (4 years) as a trainee under a certified journey level plumber, including at least 4,000 hours on commercial or industrial work.

The specialties need fewer hours: Residential (PL02) 6,000; Residential Service (PL04) 4,000; Pump & Irrigation (PL03) 4,000; Domestic Well (PL03A) 2,000.

Fees: $202.10 for the exam application, then a $242.70 certification fee for journey level, residential and residential service; the medical gas endorsement takes a $74.30 application plus $166.90.

PSI administers Washington's plumber examinations.

The exams are based on the 2015 Uniform Plumbing Code (UPC) and include amendments adopted by the Washington State Building Code Council, and the journey level and residential exams are closed book.

If you fail, you file a new $202.10 application and wait 2 weeks (14 calendar days) from your last examination before you can schedule another date with PSI.

Our research did not record a section-by-section content outline, so work from the UPC with the Washington amendments and check the candidate materials L&I points you to.

Plumber certifications renew on your birthdate every 3 years, and each renewal needs 24 hours of continuing education.

For journey level (PL01), Residential (PL02) and Residential Service (PL04), at least 12 of those hours must be plumbing code and 4 hours industry-related electrical (IRE).

Trainees are on a yearly rhythm: 8 hours of approved continuing education to renew the trainee certificate each year.

Our research did not capture the renewal fee; confirm it with L&I before your renewal comes due.

Only in one case: Washington has reciprocal certification with Idaho for journey level plumbers.

If you are certified anywhere else, you must pass the Washington exam — but while you wait, you can apply for a one-time 120-day temporary permit that costs $100.30.

Separately, the trainee-hours rule matters for anyone moving here: hours from out-of-state employers or out-of-state apprenticeship programs do not count toward certification, so the supervised hours must be earned with a Washington employer.

L&I's public lookup is the 'Verify a Contractor, Tradesperson, or Business' tool, and it covers contractor registrations and plumber certificates.

Our research recorded the tool by name but not its direct web address, so start at L&I's site — linked in the sources on this page — and follow the verification tool from there.

Check a certificate before you hire someone, and before you take a job with a shop that claims certified status.

Two specializations sit inside the plumbing certification system.

The Backflow specialty plumber certificate (PL30) requires a DOH Backflow Assembly Tester certificate.

The Medical Gas piping installer endorsement (MG01) is for journey level plumbers and requires at least 32 hours of training in an L&I-approved medical gas training course.

The plumbing certifications our research recorded for Washington — trainee, journey level and the specialty list above — include no separate gas-fitter certificate; if you will run gas piping, ask L&I which certification covers that work where you are.