Water is normally maintained at a significant pressure to enable water to flow from the tap, shower, etc. If a water main bursts, pipes freeze, or there is unexpectedly high demand on the water system, the pressure in the pipe may be reduced.
During these types of events, the pressure may be reduced enough to reverse the intended flow of water and actually draw water out of nearby service connections. If these connections are affixed to chemical mixing facilities or any non-potable water supply, the possibility exists that dangerous backflow can occur resulting in contamination of our public water supply.
What is a backflow prevention device?
This is a device that prevents water from flowing backwards into a water supply line resulting in a contaminated water supply. There are degrees of protection ranging from a vacuum breaker on a garden hose line to reduced pressure zone backflow preventers commonly used in an industrial setting where chemicals are connected to water lines. What is used and where it is installed depends on the application and the threat level.