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Backflow preventers and testing: a homeowner's guide

If your utility sent a letter about backflow testing, or you have a lawn sprinkler system, this explains what a backflow preventer is and why it gets tested.

The short answer

Backflow is water flowing the wrong way – from a hose, sprinkler system or boiler back into the drinking water pipes. A backflow preventer lets water flow one way only. Many utilities require annual testing of backflow assemblies, usually on irrigation systems, by a certified tester. Every homeowner can add a cheap hose-bib vacuum breaker to outdoor faucets.

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Backflow and cross-connections

The EPA defines a cross-connection as any actual or potential link between drinking water plumbing and a non-drinking-water source, and backflow as water flowing the wrong way through it – which can cause serious chemical or microbial contamination. The City of Bremerton, Washington gives the everyday example: if water main pressure drops while a hose sits in contaminated water, that water can be pulled backward into your pipes.

Simple steps for every home

  • Never leave a hose submerged in buckets, pools, hot tubs, sinks or a car radiator (Bremerton).
  • Put a hose-bib vacuum breaker on every outdoor faucet – Bremerton and Panama City Beach, Florida both advise it.
  • Leave the air gap at sinks and dishwashers alone – EPA describes air gaps as very effective, non-mechanical backflow preventers.

Backflow prevention assemblies

Backflow devices are designed to let water flow in only one direction, as Panama City Beach explains. Homes commonly need a testable assembly on lawn irrigation, fire sprinklers, boilers or a well connection. Panama City Beach notes that homeowners who install their own irrigation still need a suitable backflow assembly.

Annual testing

Testable assemblies have internal checks and springs that wear, so many utilities require a test every year:

  • Durham, North Carolina requires annual re-testing after installation, and gives an owner 15 days to repair or replace an assembly that fails.
  • Columbus, Ohio requires owners to hire a city-approved certified tester for annual tests and repairs.
  • San Antonio requires irrigation backflow assemblies to be tested by a licensed backflow prevention assembly tester.

Your utility’s letter will say who may test and how results are filed. Many plumbers are certified testers.

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Questions

What is a backflow test?

A certified tester checks that a backflow prevention assembly still stops water flowing backward into the drinking water supply. Many utilities require it every year.

Do homeowners need backflow testing?

Often only if you have a testable assembly, most commonly on a lawn irrigation system. Your water utility sets the rules and will usually notify you.

What is a hose bib vacuum breaker?

A small device that screws onto an outdoor faucet and stops water from being pulled back into your pipes through a hose. Utilities such as Bremerton, Washington advise one on every outdoor faucet.

Who can test a backflow preventer?

A certified or licensed tester approved by your water utility. Columbus, Ohio, for example, requires a city-approved certified tester.

Related guides

Low water pressure: find the cause in 10 minutesLow pressure at one faucet and low pressure in the whole house have different causes. Start by working out which one you have.How to find a hidden water leakA higher water bill or the sound of water running when nothing is on are the usual first clues. Your water meter can tell you in two hours whether you have a leak.Lead pipes and lead in water: how to check and what to doHomes built before 1986, especially in older cities, may have lead pipes or a lead service line. Here is how to find out and how to lower your exposure in the meantime.

Sources

Facts and figures in this guide come from these official and manufacturer sources, checked October 2026:

  1. EPA – Cross-connection control fact sheet (PDF)
  2. EPA – Cross-connection control manual (PDF)
  3. City of Bremerton, WA – For homeowners (cross connection)
  4. City of Panama City Beach, FL – Cross connection control
  5. City of Durham, NC – Annual backflow testing program
  6. City of Columbus, OH – Cross connection and backflow
  7. San Antonio Water System – Annual backflow testing

Updated October 2026 by the Plumbers Pages editorial team. General information for homeowners, not professional advice – codes and equipment differ, so follow your product’s manual and local rules. When gas, electricity, sewage or anyone’s safety is involved, call 911, your utility or a licensed plumber. How we write our guides · Plumbing glossary

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