Backflow is the undesirable flow reversal of water, liquids, gases or other substances into the public water supply.
Backflow can occur when water pressure in the distribution system drops relative to a service line. This can happen due to the use of hydrants for fire fighting, water main break, high usage, or backpressure from a pump.
A backflow assembly allows water to travel in only one direction. When working properly it stops a contaminant such as pesticides, fertilizers or animal waste from entering the potable water supply when either a backsiphonage or backpressure event occurs. A reduced pressure assembly (RPZ) is required for both residential lawn irrigation systems and when a resident uses public domestic service while also having a private irrigation well within the property limits.
To prevent backflow, most water districts are required to have a backflow prevention program in place along with backflow prevention devices which meets local plumbing and building codes. Most cities and counties in the United States require yearly testing of each water district by a certified backflow tester. When the pressure in a water system isn’t maintained, the risk for water to flow backward into the water system and become contaminated is greatly increased. Backflow testing monitors the health and safety mechanisms designed to protect water purity.