A Guide to Backflow Prevention
Understand the devices that protect your drinking water and ensure your irrigation system is safe and compliant.
What is Backflow?
Backflow is the unwanted reversal of water flow from an irrigation system back into the clean, potable water supply. This can happen in two ways: back-siphonage (caused by negative pressure in the supply line) or back-pressure (caused by downstream pressure being higher than supply pressure). Both can introduce harmful contaminants like pesticides, fertilizers, and bacteria into your drinking water.
Protection is Not Optional
Reduced Pressure Principle Backflow Assembly (RPBA / RPZ)
The RPBA is the most reliable and safest backflow preventer. It protects against both back-siphonage and back-pressure in high-hazard situations. It features two independent check valves and a pressure-differential relief valve between them, which will discharge water if one of the check valves fails, providing a visual indication of a problem.
Pros:
- Highest level of protection
- Protects against high-hazard contaminants
- Protects against back-pressure
Cons:
- Highest pressure loss
- Most expensive
- Must be installed above ground
Installation Rule: Must be installed 12" above ground. Requires annual testing.
Double Check Valve Assembly (DCVA / DCA)
A DCVA consists of two independent check valves. It protects against both back-siphonage and back-pressure but is only suitable for low-hazard (non-health hazard) applications. It does not have a relief valve.
Pros:
- Protects against back-pressure
- Can be installed below grade (in a valve box)
- Lower pressure loss than an RPBA
Cons:
- Only for low-hazard applications
- Offers no protection against health hazards
Installation Rule: Can be installed below ground. Requires annual testing.
Pressure Vacuum Breaker (PVB)
A PVB is designed to protect against back-siphonage in high or low-hazard applications. It has a spring-loaded check valve and an air inlet that opens to break the siphon when pressure drops. It offers no protection against back-pressure.
Pros:
- Protects against high-hazards (siphonage only)
- Lower cost than an RPBA
Cons:
- No back-pressure protection
- Must be installed above ground
- Can spill water during normal operation
Installation Rule: Must be installed 12" higher than the highest head or outlet. Requires annual testing.
Atmospheric Vacuum Breaker (AVB)
The simplest form of backflow prevention, an AVB is a plastic or brass device that must be installed on every zone after the valve. It only protects against back-siphonage and cannot be under constant pressure (no valves downstream).
Pros:
- Inexpensive
- Simple to install
Cons:
- No back-pressure protection
- Cannot be under constant pressure
- Must be installed on each zone
Installation Rule: Must be installed 6" higher than the highest head. Not testable.
Device Comparison
A quick-reference table to compare the capabilities of each device.
| Device | Back Siphonage | Back Pressure | Constant Pressure | Low Hazard | High Hazard | Install Rules / Notes |
|---|---|---|---|---|---|---|
| AVB | No valves downstream. Max 12 hrs pressure. Install +6" above highest head. | |||||
| PVB | "Spits" water on start. Install +12" above highest head/pipe. | |||||
| SVB | Spill-resistant (indoor use). Install +12" above highest head/pipe. | |||||
| DCVA | Can be buried (below grade). Most common for standard residential. | |||||
| RPBA | Safest device. Must be +12" above grade. No pits. High pressure loss. |
Ready for the Next Step?
You've learned the essentials. Now, let's put that knowledge to work for your lawn.
Get an Instant Estimate
Use our online tool to get a free, no-obligation estimate for your sprinkler needs in minutes.
Request Professional Service
Know what you need? Schedule a visit from our licensed technicians to get the job done right.
Explore Maintenance Plans
Protect your investment. Discover our plans for year-round care and peace of mind.