A backflow prevention assembly is used to protect water supplies from contamination or pollution due to backflow.
In water supply systems, water is maintained at significant pressure to enable the water to flow from the tap, shower, etc. When pressure fails or drops, as may happen if a water main bursts, pipes freeze, or there is unexpectedly high demand on the water system, the lower pressure in the pipes may allow contaminated water from the ground, from storage, or from other sources to be drawn into the system.
Back pressure is another means by which contaminants can enter potable-water piping. Sources of back pressure can include pumps in the water-distribution system, boilers, heat-exchanging equipment, and power-washing equipment. These devices can present an almost-constant risk of overcoming the static water pressure in the piping. To reduce the risk of contamination, a backflow preventer can be fitted. A backflow preventer can help prevent problems that might arise when chemicals are used, for instance for commercial/industrial descaling (boilers), or when bleaches are used for residential power washing.
To prevent contamination caused by back pressure, some regulatory regimes require an air gap or mechanical backflow prevention assembly fitted between the delivery point of mains water and local storage or use. Where submerged mains inflow is permitted, a backflow prevention assembly is required. This protects the potable water system from contamination hazards. These hazards can be severe, and there are more than 10,000 reported cases of backflow contamination each year. Some cases can be fatal.