A pressure vacuum breaker system uses a combination of water and atmospheric pressure to provide protection against backsiphonage (the process of water flowing backward into the potable water supply).

A reduced pressure zone backflow preventer is not all that different from a double check system. Both have two different check valves that they use to provide protection. Both valves can operate independently from one another (allowing one to close if the other malfunctions or seizes up).

Double check backflow prevention is commonly used in buildings and properties that have features that require a pretty large amount of water or that have a fairly high chance of accidental contamination.

The air gap method of backflow prevention is simple: create a gap of air between a point between the water supply and a sewage collection point.

A vacuum breaker is an attachment commonly placed on a bibcock valve or toilet or urinal flush valve, that prevents water from being siphoned backward into the public drinking water system.