Backflow frequently asked questions

Backflow is water flowing the wrong way: from a building’s plumbing back into the public water supply. It can happen when pressure in the water main drops (backsiphonage, for example during a main break or firefighting) or when pressure inside the building is higher than the supply (backpressure, for example from a boiler or pump). If the plumbing is connected to irrigation water, fertiliser, chemicals or a fire sprinkler system, that reversed flow can contaminate drinking water.

A backflow prevention assembly is a set of valves installed where your plumbing connects to a hazard (or where your service line connects to the public main). It lets water flow in only one direction and blocks it from flowing back into the supply.

Backflow assemblies contain springs, rubber seals and check valves that wear out, foul with debris or stick over time, and a failed device usually gives no visible warning. For that reason many water utilities and state regulations require testable assemblies to be tested when they are installed, after they are repaired or moved, and at least once a year after that, by a certified backflow tester. The tester submits the results to the water utility.

Usually your water utility (the "water purveyor"), as part of a cross-connection control program required by state drinking-water rules. Requirements differ from one utility to the next, so the notice or letter from your utility is the best guide to what is due and when. If you are not sure, contact us with the notice and we will help you work out what it requires.

The most common testable assemblies are the reduced pressure zone assembly (RPZ or RP), the double check valve assembly (DCVA or DC) and the pressure vacuum breaker (PVB). RPZs protect against high hazards such as chemicals and are common on commercial buildings, boilers and some irrigation systems. Double checks are used for lower hazards and many fire sprinkler systems. PVBs are mainly used on lawn irrigation systems and only protect against backsiphonage. Fire lines often use detector versions of these assemblies (DCDA or RPDA).

A routine test of a single, accessible assembly usually takes well under an hour. The water to the property, or to the irrigation or fire system the device protects, is shut off briefly while the test is performed. Time can be longer if a device is hard to reach, in a vault, or fails and needs repair.

The tester records which part failed. Most failures are fixed by cleaning or replacing internal parts such as check valve discs, springs, seals or the relief valve, using a repair kit for that make and model. After the repair the assembly is retested, and the passing result is submitted. Very old or damaged assemblies are sometimes better replaced.

No. An RPZ discharges water from its relief valve when it detects a problem, most often debris or wear on the first check valve, or pressure fluctuations on the supply side. A steady drip or a large discharge usually means the assembly needs service. Do not plug the relief valve: it is a safety feature.

Usually, yes. Most cities and water districts require a plumbing permit and an approved device type for new or replacement installations, and that work must be done by a licensed plumbing contractor (C-36). BackflowCare doesn’t install or replace devices, but we can refer you to a trusted licensed plumbing contractor, then test the new device once it’s in.

It can. A backflow assembly or check valve on the main service makes your plumbing a "closed system", so the water that expands when it is heated has nowhere to go. That can raise pressure and cause a dripping relief valve on the water heater. A thermal expansion tank is the usual fix, and some codes require one.

A standard backflow test is $199 per device. We also offer an annual Service Plan at $185 per year (cancel anytime) and a Prepaid 3-Year Service Plan at $530 ($180 per year). New customers get $25 off. Some water districts charge their own fees, such as San Francisco’s $30 tag fee, which are billed separately, and extra fees may apply to devices 2 inches or larger or that are hard to access.

Yes. After the test we submit the results to your water district in the format it requires, whether that is an online portal, email or a paper form. You can also upload your district’s notice when you book, so we have the device and account details it asks for.

Yes. California’s cross-connection control rules require backflow prevention assemblies that a water supplier requires to be tested at least once a year, whether or not the property is occupied, and again after installation, repair or relocation. Your water supplier enforces this and sends the notice, and some set their own deadlines (for example, the City of Tracy requires tests by June 30 each year).

No. A few suppliers test their customers’ devices with their own staff (for example San Jose Water and the City of Hayward), so you don’t hire a tester there. If your device fails, we can make minor repairs; a replacement needs a licensed plumbing contractor, and we can refer you to one we trust.

Your water bill names your water supplier, and its backflow test notice comes from that supplier. Some cities have more than one supplier (for example San Jose, Menlo Park and Livermore), so the city alone doesn’t always tell you. Our service areas page lists the suppliers for each city we serve.