What is a backflow preventer, and how is it tested?

A backflow preventer is a one-way valve assembly on a water line that stops water from flowing backward into the drinking-water pipes of your house. You will most often see one on a lawn sprinkler system, and a licensed tester checks it with a gauge at installation, after any repair, and at least once a year.

What backflow is, and why it matters

Backflow is the reverse flow of water or other substances in pipes, typically caused by unusual and irregular changes in pressure.^[3] It happens in two ways:

• Back-siphonage. Back-siphonage is the backward flow of water or other substances from one system to another because of a decrease in pressure.^[3]
• Backpressure. Backpressure is the backward flow of water or other substances from one system to another because of an increase in pressure.^[3]

For a sprinkler system, the stakes are practical. Chesterfield County explains that if a backflow condition were to occur, such as unexpected pressure changes from a water-main break or fire-fighting activities, your drinking water could become contaminated by fertilizers and pesticides that you apply to your lawn.^[2]

Device or assembly

Plumbers use two words that sound alike. Fairfax County's program says a Backflow Prevention Device is a plumbing valve installed in line which is NOT testable or repairable,^[1] while a Backflow Prevention Assembly is a plumbing valve installed in line which requires testing at installation, immediately following repair or relocation, AND at least annually.^[1] That is why an "assembly" is the thing that gets a yearly appointment.

The common types differ in what they stop. Chesterfield lists a pressure vacuum breaker as designed to stop back-siphonage backflow only and not usable where backpressure may develop in the downstream piping, while a reduced pressure assembly is designed to stop back-siphonage and backpressure backflow.^[2] Which one you have is set by the hazard and by your locality, so the right type is a question for your tester or building department.

What a test tells you

A certified tester connects a test gauge to the assembly and checks that its internal check valves, and the relief valve where it has one, hold. The county guide gives the pass-or-fail lines in plain numbers. For a pressure vacuum breaker, the assembly must be overhauled or replaced if tests reveal the check valve closes at less than 1.0 psi (pounds per square inch) on the test gauge.^[2] For a reduced pressure assembly, it must be overhauled or replaced if tests reveal the check valves will not hold tight or the relief valve opens at less than 2.0 psi on the test gauge.^[2]

The result is paperwork as well as a pass or fail. Test results must be recorded on an approved BFP Test Report form. The report must be signed by the tester.^[2] In Fairfax County the vendor will conduct the test, complete all paperwork, and submit it to Fairfax County,^[1] so ask your tester who files the report where you live.

If the assembly fails, the fix comes before the paperwork. In Fairfax County it must be repaired or replaced, and re-tested before a Backflow Assembly Test Report can be submitted by the vendor.^[1]

Who is allowed to test

The state's tradesman rules define a backflow prevention device worker as someone who engages in, or offers to engage in, the maintenance, repair, testing, or periodic inspection of cross connection control devices.^[4] Chesterfield County states that individuals who perform tests on backflow prevention assemblies must hold a valid Tradesman Certificate as a Backflow Prevention Device Worker issued by the Virginia Department of Professional and Occupational Regulation.^[2] State law makes the certification program voluntary so long as any requirements of the local governing body are met, and under it all local governing bodies shall accept certification by the Board of backflow prevention device workers as proof of experience and training without requiring additional examination.^[5]

You can check the tester's certification on DPOR's License Lookup before you book.^[6]

What it costs and how often

The yearly test is the price of owning the device. Read how much backflow testing costs in Virginia for what moves a quote, and whether Virginia requires annual testing for what the code and localities say.

When to call a licensed pro

For the test, and for anything that touches the assembly. Testing, repair and replacement are work for a certified tester, and Fairfax County says you must obtain either a Commercial or Residential Plumbing Permit in all instances of installation, whether as new construction or replacement.^[1] A homeowner's job is to keep the device accessible, leave it alone, and book the test. Call a certified tester when:

• The yearly test is due, or you have never had the device tested.
• The assembly drips, spits water or has been hit by a mower or freezing weather. That calls for a tester and often a repair.
• A test report says the assembly failed. It has to be repaired or replaced and re-tested.
• You find no backflow device at all on an irrigation system. Ask a licensed contractor to add one.

More in irrigation answers, or browse irrigation businesses. Read what a lawn sprinkler system needs for permits and backflow protection, then describe your job and licensed local pros can quote it.