Plumbing Contractor Requirements in Washington

Short Answer: Washington plumbing has two layers: the business registers as a contractor with L&I, and individual plumbers hold certificates of competency under RCW 18.106. Most plumbing beyond simple repairs also needs a local permit.

Quick Facts

Plumbing mistakes hide behind walls and show up later as water damage, so it pays to check a plumber carefully. Washington regulates plumbing at two levels: the business and the individual. Here is how both work and how to check them.

Two Layers of Regulation

1. The business must be registered as a contractor under RCW chapter 18.27, with a surety bond and liability insurance, like other construction contractors.
2. The individual plumber must hold a certificate of competency, or work as a trainee under the supervision required by RCW chapter 18.106.

Washington L&I lists 2,007 active plumbing contractors with a Washington address in the current file.

Step 1: Check the Business Registration

Search the business in our lists of Licensed Plumbers in Washington or on L&I Verify. Confirm the status is ACTIVE, the expiry date is after your job, and a bond and insurance are on file.

Step 2: Check the Plumber’s Certificate

Ask the person who will do the work for their certificate number and confirm it on L&I Verify. If a trainee is working on your job, ask who is supervising them and verify that person’s certificate too.

Step 3: Ask About the Permit

Many plumbing jobs, including new fixtures, re-piping, water heaters and gas lines in some areas, need a permit and inspection from your local building department. Rules vary by city and county, so ask your plumber which permits apply and who will obtain them.

Tip: Keep the permit and final inspection paperwork with your home records. Buyers, lenders and insurers may ask for it later.

What Our Plumber Lists Include

Our city lists contain businesses whose registration type or specialty is plumbing. They show the business record, not individual certificates. A plumbing business can be registered and still send someone uncertified, so step 2 matters.

Common Plumbing Jobs and What to Watch For

Water Heater Replacement

Ask whether the quote includes the permit, seismic strapping, expansion tank if required, venting changes and disposal of the old unit. Cheap quotes often omit these.

Leaks and Emergency Calls

Emergency jobs put you under pressure. Ask for the price structure up front: call-out fee, hourly rate, and when overtime rates apply. Even in an emergency, a ten-second registration check is worth it.

Re-Piping and Remodels

Larger jobs should have a written contract with scope, materials, schedule and payment terms. On remodels, the plumber is often a subcontractor to a general contractor; check them separately.

Sewer and Side Sewer Work

Side sewer and connection work is often regulated by local utilities or cities, with their own permits and approved-contractor rules. Ask your city which rules apply.

Questions to Ask a Plumber

• What is your contractor registration number?
• Who will do the work, and what are their certificate numbers?
• Does this job need a permit, and who pulls it?
• Is the quote fixed price or time and materials?
• What warranty do you offer on labor and parts?
• Will you provide lien releases for suppliers on larger jobs?

When Something Goes Wrong

If a plumber’s work causes water damage, the claim usually goes to the contractor’s liability insurer; notify your own insurer too. If the work is incomplete or defective, that is a contract matter and the bond may apply. Our guide on How to File a Claim Against a Contractor Bond in Washington explains the legal steps.

Red Flags Specific to Plumbing

• No registration number on the quote or van.
• Reluctance to pull permits for work that clearly needs them.
• Pressure to approve an expensive replacement without showing you the problem.
• Large cash deposits for routine jobs.

Before the Plumber Leaves

At the end of a plumbing job, ask for a short handover: where the shut-off valves are, what was replaced, the make and model of any water heater or fixture, and how to register manufacturer warranties. Confirm whether a final inspection has been passed and keep a copy of the permit record. Run each fixture and check for leaks under sinks and around connections while the plumber is still on site. Keep invoices showing the business name and registration number with your home records; they help with warranty claims and with questions from buyers or inspectors when you sell the house.

Bottom Line

Check the business, check the person and ask about the permit. Those three questions take a few minutes and prevent most expensive surprises.

Fixed Price or Time and Materials?

Plumbing work is often quoted in one of two ways. A fixed price covers a defined scope for an agreed amount; it suits jobs where the work can be fully seen, such as replacing a fixture. Time and materials bills hours and parts as they are used; it suits investigative work like tracing a hidden leak. For time and materials, ask for the hourly rate, the minimum charge, how parts are marked up and a not-to-exceed figure that requires your approval before it is passed.

Whichever method you choose, get it in writing before work starts, and ask for an itemised invoice at the end. An itemised invoice makes a warranty claim, an insurance claim or a later dispute far easier to resolve.

Keeping Records

Keep the contractor’s registration number, the plumber’s certificate number, the permit and inspection result, the invoice and any warranty documents in one place. Water heaters, fixtures and valves often have separate manufacturer warranties that require proof of professional installation, and the paperwork you collect on the day is usually the paperwork you will need.

How Long Does a Check Take?

Looking up a business registration and an individual certificate on L&I Verify takes a few minutes. Ask for both numbers when you book the appointment, and check them before the plumber arrives. If the business cannot give you a registration number on the phone, treat that as your answer and call someone else.

If the Plumber Is a Subcontractor

On remodels the plumbing is often subcontracted. You may never sign anything with the plumbing company, but it can still file a lien on your property if the general contractor does not pay it. Ask the general contractor for the plumbing subcontractor’s name and registration number, check it, and ask for a lien release when the plumbing work is paid for.

Where to Go Next

Before you hire, run the business through the Washington Contractor License Lookup.