A backflow test is a procedure that tests the reliability of a backflow regulator, which is designed to keep water flowing in a single direction in a plumbing system. Faulty regulators cause a potentially dangerous situation in which potable water reverses direction and can become contaminated.
Backflow regulators are required in any building with an irrigation system, fire suppression system or large boiler. Testing for such buildings must be done annually by a licensed plumber certified for backflow testing. Backflow can occur when water pressure suddenly diminishes, which can happen if there is a plumbing break in the building or within the city supply, such as a water main rupture. Municipal water supplies must be tested annually as well.