Backflow occurs when water flow is reversed from its intended direction and, buy way of a cross connection, is pushed or siphoned back into the public drinking water system. Backflow can occur by the following mechanisms:
Backsiphonage - The pressure in the drinking water system is lowered. This type of backflow can result from water line flushing, fire suppression or water main breaks.
Backpressure - The pressure in a customer's plumbing system is greater than that of the public drinking water system. This primarily occurs in commercial applications involving pumps, high rise buildings, or boilers.