Most people find out they own a backflow assembly the day a letter arrives about it. It is usually addressed to the property owner, it cites a state rule, and it has a deadline on it. If you bought the house recently, the previous owner probably never mentioned it. Nobody does.
So here is what the thing is, why the water bureau keeps writing to you about it, and what actually happens on a test.
What the letter is asking for
Somewhere on your property is a valve assembly whose only job is to stop water from running backwards out of your plumbing and into the public main. Your water provider has it in a database. Under Oregon’s drinking water rules — OAR 333-061-0070 — every approved assembly has to be tested at least once every twelve months, and only a tester certified by the Oregon Health Authority can do it.
Portland Water Bureau mails a reminder each year and suggests residential customers test in spring, once sprinklers are back on. Tualatin Valley Water District, which covers much of Beaverton and the unincorporated areas around it, has set a September 1 deadline for residential reports. Hillsboro, Tigard, Tualatin and the rest each run their own program. The date on your letter is the one that counts.
You do not mail anything yourself. The tester submits the report; Portland asks for it within 10 business days of the test.
Why your water provider cares this much
Water normally flows one way: from the main, through your meter, into the house. Two things can reverse it. A water main break or a fire hydrant opened hard down the street can drop pressure in the main enough to pull water backwards — that is back-siphonage. Or something on your side can push harder than the city supply, like a booster pump or a boiler.
Now picture what is sitting in a sprinkler line. Standing water that has been in the pipe since August. Fertilizer. Whatever the dog did on the lawn, drawn back up through a sprinkler head lying in a puddle. That is the whole reason irrigation systems need protection, and it is why a $75 test gets treated like a compliance matter rather than a suggestion.
Which assembly do you have?
On most houses around here it is one of three, and you can usually tell which from a look.
| Assembly | Where you usually find it | How to recognise it |
|---|---|---|
| Double check (DC) | In a green plastic box in the lawn, often near the meter or where the sprinkler line leaves the house | Brass body with two shutoff handles and four small test cocks along the top. Two check valves inside. The most common residential setup in the metro. |
| Pressure vacuum breaker (PVB) | Above ground, standing up on a riser beside the house | A single bonnet on top with a vent. It has to sit at least 12 inches above the highest sprinkler head it serves. |
| Reduced pressure (RP) | Above ground, never buried — on fire lines, commercial kitchens, or irrigation that injects fertilizer | Longer body with a relief valve port underneath. If it ever starts spitting water out of that port, it is telling you a check valve is not sealing. |
If you have a fire sprinkler system in the house, there is a fourth assembly on that line too, usually indoors. It gets its own test and its own line on the report.
What happens during the test
It takes 30 to 60 minutes per assembly. Your water is off for part of that.
The tester hooks a differential pressure gauge to the test cocks and checks each part does what it is supposed to. On a double check, each check valve has to hold at least 1 psi of difference across it without leaking through. On an RP, the relief valve has to open at no less than 2 psi. Those are small numbers, and a sliver of grit on a rubber seat is enough to miss them.
Pass, and the report goes to your provider. That is the end of it until next year.
Why assemblies fail
Not because they are old, mostly. An assembly that has been tested and maintained can last a very long time. The usual reasons are smaller than that:
- Debris on a check valve seat. Sand or scale from the main, often after the city has done work on your street. Sometimes cleaning it is the whole repair.
- Worn rubber. The check discs and seals are rubber, and rubber hardens. A rebuild kit replaces them without replacing the assembly.
- A tired spring that no longer closes the check firmly enough.
- Freeze damage. A cracked body, bonnet or test cock. This one usually means a new assembly, and it is the failure we see that was most avoidable.
If it fails, we show you what failed and quote the repair before touching it. Most repairs happen on the same visit. Then we retest and file the passing report, so you are back in compliance the same day.
Late October: the job worth doing this week
Portland does not freeze often. It only takes one night in the mid-20s, though, and a double check assembly is a brass body full of standing water sitting in a plastic box at ground level. Water expands as it freezes. The brass does not.
If your assembly serves a sprinkler system, once you have shut the system down for the year:
- Close the shutoff that feeds the irrigation line. It is usually in the basement or crawlspace, or in the meter box.
- Open the test cocks with a flat screwdriver so the body can drain. You will hear it gurgle.
- Turn both ball-valve handles to half-open, about 45°, so no water gets trapped behind them.
- On an above-ground PVB or RP, put an insulated cover over it. Hardware stores sell them.
- If you have the lines blown out with compressed air, make sure the air goes in downstream of the assembly, not through it.
Do not do this to a fire sprinkler assembly. That one protects the sprinkler system in your house and has to stay on and full year-round. If it sits somewhere that can freeze, the answer is heat or insulation around it, not draining it. Call us if you are not sure which assembly is which.
Reverse the steps in spring before turning the sprinklers back on, and open the shutoff slowly so you do not slam the checks. That is also a good time to book the test.
What it costs
A standard test is $75–$150 per assembly, and filing the report is included. Properties with more than one — irrigation plus a fire line is common on newer builds and in older multi-family buildings in inner Portland — get a bundled rate when we test them together.
Repairs depend on the assembly and what failed, which is why we quote them on site rather than guessing here. For regular plumbing work outside of testing, our hourly rates are published in full in what a plumber actually costs in Portland.
If you are tempted to ignore it
People do, especially on a rental or a house they just bought. The letters keep coming. Portland Water Bureau says plainly that it may shut off water service to a property where a required assembly is not tested or a correction notice is ignored, without further notice. Restoring service then waits on the assembly being tested and passing.
There is a liability side as well. Portland notes that if an assembly fails and is not promptly repaired, the owner can be held responsible for any illness or injury that results. That is rare, but it is a strange risk to carry over a test that takes an hour.
If you pulled the irrigation out years ago and the letters still arrive, call your water provider. The assembly needs to be properly removed and capped, and they will want to confirm it before taking it off their list.
Common questions
Do I really have to test every year?
Yes. It is a state rule, not a water-bureau preference. Once a year, by an OHA-certified tester, for every assembly on record.
I just bought the house. Is this my problem now?
It is. The requirement follows the property, not the person. If the sellers skipped a year or two, getting current is one visit: test, repair if needed, file.
Can I test it myself?
Only if you hold an Oregon backflow tester certification. The provider will not accept a report from anyone else, and the gauge kit is specialised equipment.
Who sends the results to the water bureau?
We do. We file with Portland Water Bureau, TVWD, or whichever provider sent your letter.
My assembly is spraying water out of the bottom. Is that an emergency?
On an RP, water dumping from the relief port means a check valve is not sealing. It is not going to flood the house, but it is wasting water and it will fail a test. Shut off the line feeding it if you can and book a repair.