Vacuum Breakers & Backflow Preventers
The purpose of a vacuum breaker or backflow preventer is to stop dirty water from being siphoned back into the clean water system. An example of where they are helpful is if you have unreliable water pressure. When the pressure drops, water headed to faucets may run backwards into the water supply. Because this is undesirable and potentially dangerous, many cities and counties require these installed in new buildings.