Backflow occurs when the normal flow of water is reversed. This reversal can happen due to loss of pressure in the water distribution system. Water main breaks, leak repairs and fire flows are examples of backflow situations.

California State Water Resource Control Board requires all water purveyors to insure backflow devices to be tested annually, under Section 64764 of the regulations. The water supplier may provide this service or they may put the responsibility on the owner of the backflow assembly.

Backflow assemblies consist of valves and mechanisms that allow water to flow only in one direction. Anything mechanical is subject to failure. Most failures are repairable depending on the age of the assembly and the environment it lives in.