How to choose a plumber in Seattle

How are plumbers licensed in Washington?

Washington regulates plumbing at the state level through the Department of Labor and Industries (L&I), under chapter 18.106 RCW. RCW 18.106.020 says no one may engage in or offer to engage in the trade of plumbing without a journey level certificate, specialty certificate, residential service certificate, temporary permit or trainee certificate, plus photo identification, in their possession. A trainee must be supervised by a certified plumber, and a contractor may not employ anyone to do plumbing unless the contractor is a licensed plumbing contractor and the worker holds one of those certificates. Each day someone advertises, bids or works in violation counts as a separate infraction.

L&I's plumber program page puts it simply: only L&I-certified plumbers can legally do plumbing work on someone else's property, while owners can do their own plumbing on property they own. L&I says it regulates more than 6,000 plumbers and 4,000 plumber trainees at any time, checks jobsites at random and investigates complaints.

How do you look up a plumber with L&I?

1. Open the L&I Verify tool. You can search by business name, contractor or tradesperson license number, or UBI number.
2. Confirm the company holds an active plumbing contractor license. L&I's Hire Smart guide for plumbing contractors says to use the same tool to make sure the contractor has a bond and liability insurance on file and no outstanding infractions.
3. Look up the individual who will do the work, not just the company. Certificates belong to people.
4. Review the history for lawsuits against the bond and past violations.

On the job, the Hire Smart guide says certified plumbers must keep their certification badge visible so customers can see they are properly certified. Ask to see it.

Does Seattle or King County add its own rules?

Not for licensing, but for permits, yes. Public Health Seattle and King County runs the plumbing permit program for Seattle, Clyde Hill and unincorporated King County, according to its permits page; other cities issue their own. Its guidance on hiring contractors says it is against the law to hire unregistered contractors or skip required permits and inspections, that all contractors who work, advertise or bid must be registered with L&I, post a bond and carry general liability insurance, and that plumbing permits may be bought by owners doing their own work or by licensed plumbing contractors. It also notes a Seattle-only rule: a gas pipe installer must be the property owner or hold a Seattle Gas Piping Mechanic License.

Side sewers are different again. In Seattle, the side sewer outside the house is permitted by Seattle Public Utilities, not Public Health; see our side sewer repair guide. Suburbs such as Bellevue, Kent and Shoreline have their own rules, covered on our location pages.

How do you compare bids?

L&I recommends interviewing several licensed plumbing contractors and getting at least three written bids. The BBB's tips for hiring a plumber add: get detailed written estimates, confirm whether a price is a flat rate that includes materials or whether materials are billed separately, and ask about bids that are unusually low or high. For each bid, check that it states:

• the exact scope of work and the materials, including brand and model for fixtures and water heaters
• whether the permit and inspection fees are included, and who will apply for the permit
• how the work will be restored, such as drywall, landscaping or pavement
• the payment schedule and the completion date

Our Seattle plumber cost guide lists typical price ranges so you can judge whether a quote is in line.

What are the warning signs?

L&I's Hire Smart guide tells homeowners to be wary of contractors who make an offer that sounds too good to be true, accept only cash, want a large deposit, or want payment made out to their own name instead of a business. In plumbing, add these:

• A refusal to pull a permit for a water heater, repipe or side sewer repair.
• A large side sewer replacement recommended without camera video you can watch and keep.
• A general contractor who plans to do the plumbing part of a remodel without a licensed plumbing contractor. L&I says that part should be subcontracted to one.

What if something goes wrong?

Registration gives you options that hiring an unregistered worker does not. L&I's Homeowner Recovery Fund can pay eligible homeowners up to $25,000, depending on available funds, when a registered contractor leaves work unfinished or defective. You must own and live in the home, the contractor must have been registered with L&I, and you need a superior court judgment against the contractor ordered after July 1, 2026; you then apply within 90 days after the case ends. Condominiums are excluded. That fund only helps if the contractor was registered, which is one more reason to check before you sign.

What about an emergency?

You can still check a license from your phone in two minutes once the water is shut off. Our emergency guide explains the first steps, and our reviews page explains how to research a company's track record.

How does this site fit in?

We are an independent guide operated by SWKM GmbH, not a contractor, and we do not perform plumbing work. If you want help, email us your neighborhood or ZIP code, the problem and a few photos. We reply by email with next steps and, where we know a licensed contractor for your area, an introduction. Run the checks on this page on anyone you hire, including anyone we mention.