There are two situations that can cause the water to go backward (Backflow):
- Back pressure may cause backflow to occur when the potable supply piping is connected to a system or fixture which exceeds the operating pressure or the supply pressure of the supply piping. Higher pressure can be caused by booster pumps, boilers, pressure vessels, or elevated piping in places such as high rise buildings or tanks. If these connections are not properly protected, potable and non-potable water or liquids can be forced into the potable supply system.
- Back Siphonage is caused by a reduced pressure in supply piping. Back siphon can be caused by undersized piping, a line repair or break that is lower than a service point, reduced main pressure due to high withdrawal rates such as firefighting or flushing water mains, or a reduced supply pressure on the suction side of a booster pump.