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 Backsiphonage?
The positive flow of water can be reversed when there is a sudden reduction in water pressure in the distribution system, such as during firefighting or when a water main breaks. This can create a suction effect, drawing the non-potable substance into the potable water system.