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.
What is Backpressure?
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.