Specific Installation Guidance

Backflow Protection


High Risk Taps

Taps used in high risk installations, such as kitchen sinks, laboratories and medical facilities are considered to be a fluid category 5 risk. Backflow protection is usually provided in the form of an AUK3 tap gap i.e. an air gap of 20 mm or twice the internal diameter of the inlet pipe, whichever is the greater. 

Where an AUK3 tap gap cannot be maintained, for example where the tap gap is compromised as a result of:-

  • the tap being lowered in any way;
  • adjustment to the spout which reduces the distance between the tap outlet and spillover level of the sink; or
  • the operation of a pull out hose attachment

An alternative form of fluid category 5 backflow protection is required.


If there are any further questions, please contact the local water undertaker for advice.



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Uncontrolled if downloaded. This is informative, non-statutory guidance and intended for general guidance purposes only; it is subject to change.

Compliance with this information should not be relied upon as guaranteeing no enforcement action will be taken by water undertakers. Water Regs UK accepts no liability for loss, indirect or consequential loss arising from or in connection with this guidance document.