A backflow prevention device is used to protect potable water supplies from contamination or pollution due to backflow.

In water supply systems, water is normally maintained at a significant pressure to enable water to flow from the tap, shower, or other fixture. Water pressure may fail or be reduced when a water main bursts, pipes freeze, or there is unexpectedly high demand on the water system. Reduced pressure in the pipe may allow contaminated water from the soil, from storage, or from other sources to be drawn up into the system.

In the absence of a backflow prevention device, your water may become contaminated from water troughs, sprinkler systems, soaker hoses, and any other outdoor connections on your property.

Below are examples of  the hose-bibb vacuum breaker. These devices are relatively easy to install and can be purchased from home improvement stores for a relatively low price. They work by allowing air to enter the water system if a siphon attempts to form. Inside is a poppet valve that is held "up" by the water pressure found in the system, closing the air entrance to the device. If the pressure in the "upstream side" is reduced to atmospheric pressure or below, the poppet valve drops and allows air to enter the system, breaking the siphon.

Please follow the manufacturer's installation guidelines to ensure that your backflow device operates correctly.

Backflow prevention

Visit the Foundation for Cross-Connection Control and Hydraulic Research  to learn more about backflow prevention.