Backflow Testing

Updated November 6, 2026

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Safety

Never bypass, disassemble, or tamper with a backflow prevention assembly; tampering can contaminate the potable supply and violates most water district codes. Keep the area around the assembly clear, do not force a stuck shutoff valve, and leave gauge readings and repairs to a certified backflow tester. If water looks discolored, smells unusual, or a cross-connection is suspected, stop using it for drinking and cooking and contact the water utility.

Before the visit

Locate the backflow assembly, commonly near the water meter, in a mechanical room, or at the irrigation connection, and clear at least three feet of access around it. Note the assembly type and serial number, have any prior test reports on hand, confirm water service is on, and secure pets. Expect the water supply to be shut off for roughly 15 to 45 minutes during the test, and plan around irrigation cycles, boilers, or equipment that depends on continuous flow.

Repair vs replace

Repair is usually the right call when a test shows a single failed check valve, a worn rubber seal or O-ring, debris caught in a seat, or a relief valve that drips only under specific conditions. If the assembly body is sound and parts are still available, rebuilding with a repair kit often restores a passing result and satisfies the annual filing requirement.

When to replace

Replacement makes more sense when the body is cracked or corroded, multiple internal components fail at once, the model is obsolete with no available parts, or repeated repairs no longer hold a passing reading. Assemblies that have frozen, suffered physical impact, or are the wrong type for the current hazard level should also be swapped for a code-approved unit.

Common issues

Symptom	Likely causes	Safe check	Stop when
Failed annual test report	Worn check valve seats, degraded rubber seals, debris in the valve, or a stuck relief valve.	Review the tester's gauge readings and note which check or relief valve failed; keep the report for the water district filing.	The assembly shows no margin on either check, leaks continuously from the relief port, or the district flags the property as non-compliant.
Water dripping from the relief valve or vent	Fluctuating inlet pressure, a fouled first check valve, or a worn diaphragm in an RPZ assembly.	Watch whether the drip occurs only during pressure swings, such as irrigation startup or appliance use, or runs constantly, and note the volume.	Discharge is constant, more than a slow trickle, or the area around the assembly stays wet long enough to cause damage or ice.
Discolored or odd-tasting tap water	A cross-connection pulling irrigation water, boiler chemicals, or stagnant line water back into the potable supply.	Run a cold tap for several minutes and compare clarity and odor; check whether the issue appears only when irrigation or a boiler runs.	Water stays discolored, smells of chemicals or sewage, or anyone reports illness; shut off drinking use and call the water utility immediately.
Notice from the water district about a missing or overdue test	A missed annual filing, an unregistered assembly, or a test report that was never submitted after installation.	Confirm the assembly's serial number and location, and check whether the notice lists a compliance deadline.	The deadline is within a few days or the district threatens service interruption; schedule a certified test right away.
Visible corrosion, cracks, or damage on the assembly	Age, freeze damage, sun exposure on plastic bodies, or physical impact from mowers, vehicles, or landscaping work.	Inspect the exterior for cracks, mineral crust, or bent piping without touching valves or test cocks.	The body is cracked, fittings weep, or the assembly has shifted on its piping; keep the area clear and arrange an inspection.
Low water pressure after the assembly	A partially blocked check valve, debris buildup, or an undersized or failing assembly restricting flow.	Compare pressure at a faucet near the meter with one far from it, and note whether pressure drops when irrigation runs.	Pressure loss is sudden and severe, or fixtures sputter with air, which can signal a valve stuck nearly closed.