Plumbing guide

Backflow Preventers for Sprinklers and Reclaimed Water

A backflow preventer is a one-way gate for your drinking water. It sits on the sprinkler line and keeps lawn water, fertilizer and reclaimed water from flowing backward into the pipes you drink from.

By the Urban Comfort Plumbing team · October 27, 2026

What backflow is

Water normally flows from the city main into your house. If pressure in the main drops, because of a main break or heavy demand such as firefighting, water can flow the other way. Backsiphonage pulls water backward through a connection. Backpressure pushes it backward when a system downstream has higher pressure than the supply.

A sprinkler system is a risk because it connects to the drinking water supply and sits in the yard, where heads and valve boxes can fill with puddled water, fertilizer, pesticides and soil. Without a barrier, that water can be drawn back into the line.

How a backflow preventer works

The device contains check valves, spring-loaded gates that open to let water through and close when flow reverses. Higher-protection devices add a relief valve that opens and dumps water if the checks fail. The common types for irrigation include the pressure vacuum breaker, the double check assembly and the reduced pressure zone assembly. Which one is required depends on the hazard and on local rules.

Hose bibs have a simple vacuum breaker built in or screwed on. Fire systems, boilers and commercial buildings often need larger assemblies. A plumber can tell you what your property needs and whether it is installed correctly.

Annual testing

Many water utilities require backflow assemblies to be tested each year by a certified tester. The tester checks that the check valves hold and that the relief valve opens at the right pressure, then files a report with the utility. A device that fails needs repair, often a new seat, disc or spring, or replacement.

Keep the report. Ask the tester whether they file it for you. Clear the area around the device and make sure the cover opens. Water to the sprinkler line will be off for a short time during the test. See backflow testing and prevention for what to expect.

Reclaimed water in St. Petersburg and Largo

St. Petersburg runs a reclaimed water system for irrigation in parts of the city, and the City of Largo supplies reclaimed water for watering lawns and some business use. Reclaimed water is recycled wastewater. It is treated, but it is not meant for drinking, and its pipes must be kept completely separate from the drinking water supply.

In Florida, reclaimed pipes are commonly marked purple. A cross-connection between a reclaimed line and a drinking line is a serious hazard. If your property has reclaimed water, a plumber can check that the two systems are separate and that the backflow protection on the drinking side is in order. For the local picture in Largo, see plumbing in Largo.

When reclaimed water has problems

Reclaimed water systems can fall short of standards. In November 2019, the City of Largo told reclaimed water customers to stop using it after the city found it was not meeting disinfection standards, and it said drinking water and indoor tap water were not affected. The notice is an example of why the separation matters.

If a utility issues a notice, follow it. Turn off irrigation as directed, and do not use reclaimed water for anything other than its approved uses.

Cross-connections inside the house

Backflow risks are not only outside. A hose left in a bucket, a sink with a spray hose that dangles in the water, a hose connected to a chemical sprayer, or a fish tank siphon can all draw water backward. An air gap, a physical space between the faucet and the water in the sink, is the simplest protection.

Use a hose bib vacuum breaker on any spigot that you attach a hose to, and do not leave hoses submerged. A plumber can check the spigots and the fixtures for places where a cross-connection is possible.

Choosing a tester

Testing must be done by a person with the right certification, using a calibrated test kit. Ask for the tester's certification number and ask whether the report will be filed with the utility. A repair, if needed, should be quoted before it starts, and the device should be retested after the repair so the report shows a pass.

Ask the utility for a list of requirements, such as which devices need an annual test, and where the report goes. That avoids penalties and keeps the water supply protected.

Signs your device needs attention

Water spitting from the relief port, a cracked body, a handle that will not turn or a device that has been hit by a mower or a vehicle all need attention. A wet patch around the box, or sprinkler heads that stay wet, can mean a leak. After a flood, a device that was underwater should be checked, since debris and contamination may have entered.

Why this protects the neighborhood too

A cross-connection on one property can affect others. If the main loses pressure, contaminated water can be drawn back into the lines that serve the whole street. That is why utilities set testing rules and why a failed device is treated as a public health issue, not only a private repair. Keeping your device in good shape protects the people next door as well as your own family.

Winter, storms and the device

Florida rarely sees freezes, but a hard cold snap can crack an exposed assembly, so cover it when a freeze is forecast. After a hurricane or a flood, check the device for damage and debris, and have it retested if it was submerged. A lawn crew can also knock a device off its mounting, so mark it with a stake that the mower will not clip.

What to do now

Find your device. It is usually a pipe assembly above ground near the house or the meter, or in a box in the lawn. Note the make and size and when it was last tested. If you have a notice from the utility, call a certified tester promptly, since deadlines apply.

If you are installing a sprinkler system or adding reclaimed water, plan the backflow protection from the start and ask who handles the permit and the test report. A plumber can also check the outdoor spigots, since a leaking spigot is often related. See faucet and spigot repair.

Common questions

Backflow preventer questions

Do all sprinkler systems need a backflow preventer?

Most in-ground systems do. Local code decides which type. Ask your utility or a plumber.

How often does a backflow device need testing?

Many utilities require an annual test by a certified tester. Ask your water provider.

Is reclaimed water safe to drink?

No. It is for irrigation and some business uses, and its pipes must never connect to drinking water.

What happens if the device fails the test?

It needs repair or replacement and a retest. The utility may set a deadline.

Backflow test due, or not sure what you have?

Call and describe the device. The dispatcher will connect you with a local contractor.

Call (727) 555-0100