Water Supply Industry Interpretations and Advice

  • Area of Interest : Backflow Prevention
  • Topic : Fluid category
  • Title : WCs
  • Clause Reference : Regulation 4 & Schedule 2 paragraph 15
  • Reference Number : B58
  • Decision Date : March 2014

Although a Type AUK1 air gap must incorporate a Type AG air gap the Regulators’ Specification (test code sheet 2212.3 Annex B) permits the installation of an alternative fluid category 3 backflow prevention arrangement for WC flushing cisterns only.

In recognition of this, where an inlet feeding a WC flushing cistern fails to meet the requirements for a Type AG air gap (please refer to interpretation E04) water suppliers may be willing to accept an alternative fluid category 3 backflow prevention device in place of a Type AG air gap. This will however be dependent upon a risk assessment of the WC. Factors that will be taken into consideration will include, but are not restricted to whether:-

  • the cistern incorporates an outlet control which ensures the pipework connecting the pan and cistern is completely evacuated between flushes; and
  • if there is any risk of back pressure.

[Also see interpretation E03]