A. Backflow is possible in two situations, backsiphonage and backpressure. When there is a sudden reduction in the water pressure in the distribution system, such as during firefighting or when a water main breaks, water flow can be reversed. This can create a suction effect, drawing the non potable substance into the potable water system. A. Backpressure is created when pressure in a nonpotable system, such as in a recirculating system containing soap, acid, or antifreeze, exceeds that in the potable system that provides make up water to the system. This can force the potable water to reverse its direction of flow through the cross connection.
Nonpotable substances can then enter the potable water system.
The Environmental Division will determine which type of protection is required based on the degree of hazard that the property represents to the potable water supply. A backflow preventer is an approved, testable assembly which uses valves, in different configurations, to prevent polluted or contaminated water from reversing direction and flowing backward. A. An approved backflow prevention assembly has gone through an approval process at the Foundation for Hydraulic Research and Cross Connection Control at the University of Southern California. Only assemblies completing the entire testing procedure are recognized by Tempe Water as approved backflow prevention assemblies. A. Federal and State law require that water suppliers protect their water systems from contamination.