A backflow preventer is a device that’s installed on your home’s water pipes that allows water to flow in one direction but never in the opposite direction. It 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 an unexpectedly high demand on the water system (for example, when several fire hydrants are opened). 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.