Backflow Prevention

All backflow prevention assemblies must be tested annually at spring start up for proper operation and protection.

All Lawn Irrigation Systems Require Backflow Prevention!


Lawn irrigation systems make watering lawns and gardens easier, save you time, and can be designed to be water efficient. However, water contaminated by weed killers, fertilizers, and animal waste can backflow into your drinking water. To protect your drinking water from potential contamination, it is important to have an approved backflow protection assembly on your irrigation system. Lawn irrigation systems do require special equipment to prevent contaminated water from siphoning back into your home plumbing and public water systems.

  • Approved Backflow Assemblies installed in conformance with Idaho Plumbing Bureau requirements
  • Double Check Valve assembly (grandparented)
  • Pressure Vacuum Breaker
  • Atmospheric Vacuum Breaker

A lawn irrigation system not protected by an approved backflow prevention assembly endangers the health of a household, neighborhood, and community!

Testable assemblies must be tested by an Idaho licensed backflow assembly tester upon installation. All assemblies must be retested at a minimum annual frequency. Assemblies protecting the potable supply from irrigation must be tested each spring before the irrigation system is pressurized.

How does backflow happen?

Backflow is water flow in reverse direction from the normal direction of flow in a piping system. This occurs due to different pressures existing between two different points within a piping system; water of a higher pressure flowing to water of lower pressure.

Backflow may occur due to either backsiphonage or backpressure.

Backsiphonage – is caused by negative pressure in the piping system.

  • A water line repair or break that is lower than a water service point.
  • A lower water main pressure due to a high water usage rate such as in fire fighting or water main flushing.
  • Reduced water supply pressure on the suction side of a water booster pump.

Backpressure – occurs when the water supply piping is connected to a piping system or plumbing fixture which exceeds the operating pressure of the water supply piping.

  • Booster pumps
  • Water supply line connections to a boiler or other heating systems where thermal expansion is possible
  • Connecting to a water system that operates at a higher pressure