BACKFLOW PREVENTERS
Irrigation backflow prevention devices are installed on your home's water lines to allow water to flow in one direction, but never in the opposite. It's sole job is to protect against both back-siphonage and back-pressure of contaminated water to the potable water supply. Backflow preventers provide protection from non-potable water contaminating potable water that would cause a health hazard.
Backflow preventers are typically required by law in certain settings, especially where there's a risk of contamination (e.g., hospitals, industrial sites, irrigation systems).