Backflow, sprinklers and your water supplier

Your water supplier runs the cross-connection program under WAC 246-290-490, and for an in-ground sprinkler system that can mean a plumbing permit, an approved assembly and a yearly test by a certified tester.

Revised November 4, 2026

What is a cross connection?

It is a link between drinking water pipes and anything that could contaminate them. Tacoma Water calls a garden hose the most common potential one. It turns into an actual one if connected to a fertilizer sprayer or dropped in a pool or hot tub. Backflow is what happens when water runs the wrong way through that link. An irrigation system, Tacoma Water says, can contaminate your water and may need an approved assembly or device.

Who makes the rules?

Your water supplier, within state limits. WAC 246-290-490 says the purveyor must develop and implement a cross-connection control program, may be stricter locally, and must coordinate with the authority having jurisdiction. So two neighbors with different suppliers can have different terms. If you don't know yours, start at find your water supplier.

The state's Group B guidance says a certified backflow assembly tester must test any backflow device, and assemblies should be tested at least annually. A DOH guidance document's page says a purveyor may accept an approved atmospheric vacuum breaker on a residential irrigation system if properly installed under the UPC. That word is "may", so ask.

How does it work under Tacoma Water?

Tacoma Water publishes the fullest local account. Treat these as Tacoma's terms, not a statewide rule.

• First step: a plumbing permit, usually from your city or county building department. Tacoma Water remains responsible for all cross connections.
• Who installs: Tacoma Water says three entities can legally install these assemblies, namely the owner, a licensed plumber, or a full-time employee of the owner.
• After install: a Washington-certified tester inspects, then tests each year. A repair or replacement needs a new inspection.
• Reminders: Tacoma Water has a free program that lets your chosen tester know when a test is due.
• Unused systems: an irrigation system you no longer use still needs testing while it is physically connected.
• Skipped tests: these can draw a $100 fee per assembly, added fees, a reduced pressure assembly at the meter at your expense, or termination of your water service.

What should you do about a garden hose?

Keep the end out of pools, hot tubs and buckets of anything, and don't run a fertilizer sprayer without asking your supplier what device it accepts. That is the plain reading of Tacoma Water's example. The hose also matters in winter; the freeze page covers disconnecting it.

Where do I find the permit and the tester?

The permit comes from your local counter, listed in plumbing permits, office by office. The tester holds a separate state certification, so a plumber's certificate is a different check; see how to check a plumber. Before trenching for a new sprinkler line, call 811. On a bluff lot, Ecology says to avoid irrigation between your home and the edge, as noted under bluffs and shorelines.

Find out which assembly your supplier accepts before buying, because the supplier and the permit decide this. One place to compare the types is a page of backflow preventers. PlumbingSupplyAndMore and this atlas are run by the same team.