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.
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.