Data sources: State plumbing boards, ICC, IAPMO, EPA Last verified: 2026-03-17

Plumbing Code

Washington follows the Uniform Plumbing Code (2021 edition).

The UPC (Uniform Plumbing Code) is maintained by IAPMO (International Association of Plumbing and Mechanical Officials) and is primarily used in western states. It covers similar topics to the IPC with some differences in pipe sizing and fixture requirements.

Backflow Prevention Testing

Annual testing is required in Washington for testable backflow prevention assemblies (RPZ, DCVA, PVB).

• Residential: May be required for homes with irrigation systems or other cross-connections; check local water-supplier rules
• Who can test: Certified tester
• Enforcement: State Dept of Health; local water systems

Water Heater Installation

A permit is required to replace or install a water heater in Washington.

• Licensed plumber required: Yes
• Homeowner can DIY: No - licensed plumber required
• Seismic strapping: check local code for whether your water heater must be secured with upper and lower straps
• Note: Seismic strapping required in seismic hazard zones; licensed plumber required

Universal requirements (all states):

• Temperature & Pressure Relief (TPR) valve must be installed
• Discharge pipe from TPR must terminate safely
• Gas water heaters: proper venting required
• Gas water heaters in garages: an 18" elevation of the ignition source above the floor may apply, subject to equipment exceptions and local code
• Expansion tank often required when backflow preventer is installed on main supply

Homeowner DIY Plumbing Rights

Washington requires a licensed plumber for plumbing work. Check whether a homeowner exemption applies to plumbing on your own residence; permits and inspections are usually still required.

Check the applicable state and local licensing rule for the planned plumbing work

Water Conservation Requirements

Washington has state-level water conservation requirements that exceed federal minimums.

State water conservation standards tied to building codes

Lead Service Line Replacement

Under the EPA Lead and Copper Rule Revisions (2021), water systems in Washington must inventory service lines; the Lead and Copper Rule Improvements (2024) add requirements to replace lead service lines. Ask your water system for its inventory and replacement plan.

Important Disclaimer

This information is provided as a general overview. Plumbing codes and regulations can vary significantly between municipalities within Washington. Always check with your local building department before starting any plumbing work. Local codes override state minimums - your city or county may have stricter requirements.

Sources

• State plumbing boards and licensing agencies
• International Code Council (ICC) - IPC adoption map
• International Association of Plumbing and Mechanical Officials (IAPMO) - UPC adoption
• Manual de control de conexiones cruzadas de la EPA (guía de la Ley de Agua Potable Segura)
• State building departments

Sources

• Washington state plumbing board and licensing agency
• International Code Council (ICC) - IPC adoption map
• International Association of Plumbing and Mechanical Officials (IAPMO) - UPC adoption
• EPA Cross-Connection Control Manual (Safe Drinking Water Act guidance)
• State and local building departments