This is the method of utilizing a physical separation between the free flowing discharge end of a potable water and an open water receiving vessel. An approved airgap shall be at least double the diameter of the supply pipe, measured from the overflow rim of the vessel to the discharge pipe. In some cases, this distance may need to be greater. This is a method of backflow prevention, meaning it does not employ a special device.

Reduced Pressure Zone Assembly (RPZ)

This is an assembly of devices consisting of two independent check valves with an independent pressure differential valve located between the two check valves. This device is designed to protect against non-health (pollutants) or health (contaminants) hazards in back-pressure or back-siphon situations.

Double Check Valve Assembly (DCVA)

This is an assembly similar to the "RPZ" in that it also has two independent check valves. It does not have the pressure differential valve, which allows this device to be used only in non-health hazards situations.