Plumbing licensing is set by each state (and in some places by a city). This explainer covers Washington State only, where plumbers are certified by the Department of Labor & Industries (L&I). It answers one practical question from L&I's own pages: can you start working in plumbing before you are a certified plumber, and what does the trainee certificate require? Nothing here describes a rule change, and nothing here applies to any other state.
Is certification required to do plumbing work in Washington?
Yes, for the plumbing trade. L&I's Plumber Certification page states: "You must be certified by the Washington State Plumber Certification Program to work in the plumbing trade in Washington."
The same page sets a limit on that rule: "Except for domestic pump and pump and irrigation systems, certification is not required to install plumbing systems outside of a building (e.g., water lines connected directly to municipal water mains, sewer line connections, etc.)."
L&I's About the Plumber Program page adds two sentences about whose property the work is on: "Only L&I-certified plumbers can legally perform plumbing work on someone else's property." and "Property owners can perform their own plumbing work on properties they own."
Where do new plumbers start?
As a trainee. Under Certification Requirements, L&I states: "To become a certified journey level or specialty plumber in Washington, you must typically begin as a plumber trainee."
L&I's Plumber Trainee page lists what trainees must do, including:
- "Be 16 or older."
- "Work under the direct supervision of a journey level or certified plumber."
- "Take 8 hours of approved continuing education instruction yearly to renew their certificate."
How long is the trainee certificate good for?
One year. The Plumber Trainee page states: "Your plumber trainee certificate is good for 12 months from the date your application is approved."
For renewal, the same page says "8 hours of approved continuing education is required each year" and gives a two-year breakdown: "Within a two-year period you must take a minimum of 8 hours of plumbing code training and 4 hours of industry-related electrical (IRE) training." It continues: "The other 4 hours may be from any category: plumbing code, IRE, or industry-related plumbing (IRP)."
How are trainee hours reported?
By affidavit. L&I states: "Plumber trainees must report their supervised work hours at least once a year by filing" affidavits of experience (form F627-004-000) with L&I, and "Affidavits should be sent in no later than 30 days after your renewal date."
Trainees with more than one employer or supervisor file more than one: "Trainees must submit separate, notarized affidavits to report hours worked for each employer, registered contractor, and/or supervising plumber during the previous year."
Which hours do not count?
L&I's Plumber Trainee page states: "Trainees may not receive credit for any hours of experience:"
- "If they are not properly supervised."
- "From incorrectly completed affidavits of experience."
- "While their certificate is expired or inactive."
- "If they have outstanding penalties."
- "While working for out-of-state employers."
- "From out-of-state trainee or apprenticeship programs."
How many hours lead to a plumber certificate?
It depends on the certificate. Two examples from L&I's Certification Requirements:
- Journey level plumber (PL01). "Four years or more (at least 8,000 hours) working as a plumber trainee under the supervision of a certified journey level plumber." L&I adds: "Two years or more (at least 4,000 hours) must be spent working in commercial or industrial installations".
- Residential (PL02). "3 years or more (at least 6,000 hours) working in the specialty under supervision of a certified residential or journey level plumber." L&I says this specialty "is limited to installation, maintenance, and repair of plumbing in single-family dwellings, duplexes, and apartment buildings which do not exceed three stories."
L&I lists other specialties (residential service, pump and irrigation, domestic well, backflow and medical gas) with their own requirements; read the Plumber Certification page for those.
Where to check before you act
These are L&I's requirements as shown on its pages on the date above. L&I's pages are the authority, so confirm the current requirements there before you apply or count hours. Plumbing licensing is a planned topic on goraedu; see all certifications for its status.
goraedu is independent and is not affiliated with or endorsed by the Washington State Department of Labor & Industries or any government agency.