The short answer: if your property has a testable backflow assembly, Washington requires it to be tested by a state-certified Backflow Assembly Tester when it’s installed, after any repair or relocation, after a backflow incident, and at least once a year. Your water purveyor enforces the rule and sets your due date.
Why the rule exists
Public water systems are pressurized so water flows toward your property. When that pressure drops, during a main break, firefighting or heavy demand, water can be pulled backward out of homes and businesses into the public supply. That’s called backflow, and the pipe connections that make it possible are called cross-connections.
To protect everyone’s drinking water, Washington’s drinking-water regulations (WAC 246-290-490) require public water systems to run a cross-connection control program. That program is why your purveyor (the city, water district or PUD that supplies your water) tracks backflow assemblies and asks for test reports.
Who needs a backflow test
You need annual testing if your property has a testable backflow assembly. The most common reasons one is installed:
- Lawn and landscape irrigation systems
- Fire-sprinkler systems
- Boilers and hydronic heating
- Pools, hot tubs, ponds and fountains with automatic fills
- Restaurants, espresso and soda systems
- Medical, dental and veterinary offices
- Labs, car washes and industrial processes
- Multifamily and mixed-use buildings
Not sure whether you have one? Your purveyor’s notice will name the assembly type, size and location. Our assembly identification guide can also help.
How often testing is required
| Situation | Test required? |
|---|---|
| New assembly installed | Yes, before the purveyor accepts it |
| Every year after installation | Yes, at least annually |
| Assembly repaired, reinstalled or relocated | Yes, right after the work |
| After a backflow incident | Yes |
| Purveyor requests it | Yes, some high-hazard sites may be tested more often |
Who is allowed to test
Only a Backflow Assembly Tester (BAT) certified by the Washington State Department of Health. Certification requires passing written and hands-on exams, and testers must use test equipment that is regularly verified for accuracy. Purveyors will reject reports from anyone else, and many keep a list of testers they accept.
When you hire a tester, it’s fair to ask for their BAT certification number. It will also appear on your test report.
Premises isolation vs. in-premises protection
There are two layers of protection, with different people responsible:
- Premises isolation is an assembly at or near your service connection that protects the public system from your entire property. Your purveyor decides when it’s required, usually based on the hazard your property presents.
- In-premises protection protects people inside a building from hazards within it, like a boiler or a chemical dispenser. That’s governed by the plumbing code and your local plumbing official.
Either way, if it’s a testable assembly, it needs annual testing, and we can handle both.
Notices, deadlines and shut-offs
Most purveyors mail a test notice a few weeks before your due date, followed by reminders if no report arrives. If an assembly still isn’t tested, purveyors have the authority to take enforcement action, which can include shutting off water service until the assembly passes.
Got a final notice? Call us at (206) 549-4992. We’ll prioritize your test and file the report the same day it passes.
Owner checklist
- Find your notice (or the assembly’s test tag) and note the due date.
- Make sure the assembly is reachable: clear the valve box, unlock the room, note gate codes.
- Book a certified tester well before the due date.
- If it fails, approve the repair quote so it can be fixed and retested.
- Keep a copy of the passing report for your records.
- Put next year’s date on your calendar, or let us track it for you.
Frequently asked questions
Is backflow testing required for homes in Washington?
Yes, if the home has a testable backflow assembly, most often on a lawn irrigation system. Homes without a testable assembly generally don’t need a test.
Can I test my own backflow assembly?
Only if you’re a DOH-certified Backflow Assembly Tester with approved, accuracy-verified equipment. Purveyors won’t accept results from anyone else.
How much does a backflow test cost?
It depends on the assembly type, how many you have and how easy they are to reach. Testing several assemblies in one visit lowers the cost per assembly. Ask us for a quote.