Air gap


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Terms & Synonyms

Official WHO Definition

The vertical unobstructed air space between the water outlet and the maximum flood level, or highest possible water level of a plumbing fixture, or appliance to which the water outlet is discharging (American Society of Sanitary Engineering 1971). A physical separation between a safe drinking-water system and above the flood level of the receptor. The separation should be at least twice the supply pipe diameter, but never less that 25 millimetres (1 inch) (WHO 2006).

Other Definitions


Interpretations and Explanations

An air gap is used to ensure that the integrity of a drinking water supply is protected from a reverse flow of non drinking water, either directly, or through a siphon action into the drinking water supply. This is the simplest effective form of backflow prevention. All water supply plumbing codes require backflow or reverse flow prevention. An air gap is one way to achieve that (World Plumbing Council Working Group 2008).


American Society of Sanitary Engineering (2007) Plumbing Dictionary, 6th ed. WHO (2006) Health aspects of plumbing

WHO Lexicon page (translations and examples)

See also

External Resources


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