Do you like having water to drink? Most of us do. So, don’t contaminate it. When contaminated water goes into a water system where potable water comes out, this is called backflow. This can happen for a few reasons. Sometimes it’s due to reduction of needed water pressure either further down the line or from the water main. Perhaps there’s a fire or a water-main break. Basically, there would be more water leaving a system than being supplied. This causes a change in pressure that can reverse the flow of water, sucking in unwanted contaminates.
Atmospheric vacuum breakers are used to stop this unwanted reverse in flow in homes. To stop the reverse flow, they allow air in breaking the siphon effect. These devices are need to be six inches above grade and higher than another downstream element of the system. Because of their simple design, they typically have a long lifecycle and don’t need much maintenance.