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How to Choose a Backflow Preventer
The right assembly depends on the hazard level and your local code. A pressure vacuum breaker (PVB) is the most common choice for residential irrigation and must be installed at least 12 inches above the highest sprinkler head; it guards against back-siphonage but not back-pressure. A reduced-pressure (RP) assembly gives the highest level of protection — for high-hazard connections and anywhere back-pressure is possible. A double-check assembly covers low-hazard backflow.
Always confirm the required type, size, and testing rules with your local water authority before you buy. In freezing climates, drain the assembly or wrap it in an insulated freeze bag before winter — the exposed brass body and test cocks crack first. A backflow preventer mounts upstream of the valve manifold — for sizing the box that protects it, see our How to Choose a Sprinkler Valve Box guide.
Backflow Preventer FAQ
Do I need a backflow preventer for my sprinkler system?
Most local codes require one so irrigation water cannot siphon back into your drinking supply. The required type and size depend on your code and the hazard level — confirm with your local water authority before you buy.
PVB or RP — which do I need?
A pressure vacuum breaker is the most common choice for typical residential irrigation and must sit at least 12 inches above the highest head. A reduced-pressure (RP) assembly offers the highest protection for high-hazard connections and anywhere back-pressure is possible. Your local code sets the requirement.
How do I keep a backflow preventer from freezing?
In freezing climates, shut off and drain the assembly before winter, or wrap it in an insulated freeze bag. The exposed brass body and test cocks are the first parts to crack.
Does a backflow preventer have to be tested?
Many jurisdictions require testable assemblies to be tested by a certified tester at installation and then annually. Check your local water authority’s rule.
What size backflow preventer do I need?
Match the assembly to your service or mainline size — commonly 3/4 in or 1 in for residential irrigation. Sizing larger than the line adds cost without adding flow.
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