Air gap (plumbing)

An air gap, as related to the plumbing trade, is the unobstructed vertical space between the water outlet and the flood level of a fixture.

[1] Air gaps of appropriate design are legally required by water health and safety regulations in many countries.

A common use of the term "air gap" in domestic plumbing refers to a specialized fixture that provides backflow prevention for an installed dishwasher.

When installed and maintained properly, the air gap works as described above, and prevents drain water from the sink from backing up into the dishwasher, possibly contaminating dishes.

According to the International Residential Code 2003, an air gap length must meet the requirements of being two times the effective inner diameter of the pipe (2×D) in order to be sufficient.

Water cannot flow from the sink to the tap in normal circumstances, even if the water supply loses pressure.