How to verify a plumber in Washington
Washington has two separate checks that matter, and both are public. The plumbing company registers with the Department of Labor and Industries as a contractor, and the plumbers doing the work carry individual state certification under RCW 18.106. A legitimate operation clears both.
The contractor registration check
Ask the company for its contractor registration number, then look it up on the L&I Verify tool. It takes under a minute and the record shows:
- Active or suspended: the single most important line on the page
- Bond and insurance: registered contractors carry both, and the lookup confirms they're current
- Registration history: how long they've been on the books and whether the registration has lapsed
- Violations: infractions and unpaid-wage findings on file
A company that can't produce a registration number isn't licensed to do plumbing work for hire in Washington. That's the whole screening test.
The certification check
The person doing the actual plumbing holds an individual certificate: journey level or specialty (residential, backflow, pump and irrigation). You can ask who'll be doing the work and verify that name through the same L&I lookup. Trainees are legal only when supervised by a certified plumber on the job.
What the checks don't cover
Registration tells you the company is on the state's books and bonded. It doesn't tell you they're good at the work, that their price is fair, or that they'll treat the house well. For that part you still want a written scope, a price before work starts, and the permit answer from the permit guide. But the sixty-second check filters out the worst category: the ones who were never on the books at all.
Red flags that end the conversation
- No registration number, or a number that comes back suspended or belonging to a different company
- A quote that can't say who does the work or won't put the scope in writing
- Pressure to skip the permit on work that plainly needs one. In King County that permit runs through Public Health, and dodging it leaves the uninspected work in your walls
