Backpressure is created when the pressure in a non-potable system, such as in a recirculation system containing soap, acid, antifreeze, or in a boiler system exceeds that in the potable water system that provides the make-up water to the system. This pressure can force the potable water to reverse its direction of flow through the cross connection. Non-potable substances can then enter the potable water system.
What is a Cross Connection?
A cross connection is the actual physical connection between potable (drinking) water and any substance of questionable quality. A cross connection commonly occurs when a water hose is left running, yet is submerged in a tree well or in a bucket of soap water. If a backflow event were to occur, these substances could enter the drinking water supply and possibly be distributed throughout the distribution system where numerous consumers would be exposed to these substances.