Plumbing service
Backflow testing
Short answer
A backflow preventer stops water from flowing backward from your property into the public water supply. Many water utilities require testable devices, which are common on irrigation systems, fire sprinklers and commercial buildings, to be tested each year by a certified tester, with the results reported to the utility.
Updated · Editorial team; not yet technically reviewed
Backflow Testing at a glance
- Common locations
- Lawn irrigation, fire sprinkler lines, commercial and multi-unit buildings, boilers.
- Device types
- Reduced pressure zone (RPZ), double check valve assembly, pressure vacuum breaker.
- Testing
- Often annually, by a certified backflow tester; the report goes to the utility.
- If it fails
- It's repaired or rebuilt and retested.
What backflow is
Normally water flows from the utility's main into your plumbing. Backflow is the reverse. It can happen by back-siphonage, when a main break or heavy firefighting drops the pressure in the main, or by backpressure, when a pump or boiler on the property pushes water back. Either way, water that has sat in irrigation lines, boilers or process equipment could enter drinking water.
Types of backflow preventers
| Device | Protects against | Typical use |
|---|---|---|
| Reduced pressure zone (RPZ) | High-hazard backflow; discharges water if it fails | Commercial, medical, irrigation with chemical injection |
| Double check valve assembly | Lower-hazard backflow | Fire sprinklers, some irrigation |
| Pressure vacuum breaker | Back-siphonage | Residential irrigation (installed above the highest head) |
| Hose bib vacuum breaker | Back-siphonage at a hose | Outdoor faucets |
Backflow on home irrigation systems
Lawn sprinkler systems are the most common reason a homeowner has a testable backflow device. Sprinkler lines sit in soil where fertilizer, pesticides and animal waste are present, so codes require protection between them and the drinking water. In freezing climates, the device is usually drained or removed before winter, since an above-ground assembly can crack when water inside it freezes. That's a common cause of failed spring tests.
How testing works
Notice
Many utilities send a reminder when your test is due.
Test
A certified tester attaches a gauge kit to the device's test cocks and checks each check valve and relief valve. Water is briefly shut off.
Report
The tester submits results to the utility, often online.
Repair if needed
Failed devices are cleaned, rebuilt or replaced, then retested.
What affects the cost
- The test itself, often a flat fee per device
- Number and type of devices on the property
- Repair kits and labor if a device fails
- Full replacement of old or unrepairable assemblies
- Freeze protection for above-ground devices in cold climates
We don't publish prices; they vary by market. Get a written quote first.
Common questions
Can I test my own backflow preventer?
Utilities that require testing generally require a certified backflow tester using calibrated equipment, and the tester submits the report.
Do homeowners need backflow testing?
If you have a testable device, most often on an irrigation system, many utilities require an annual test. Your utility's cross-connection control program will say.
Why is my backflow preventer leaking?
An RPZ may discharge water when a check valve is fouled or worn, or after a pressure fluctuation. Persistent discharge needs a tester or plumber to rebuild it.