Specific Installation Guidance

Backflow protection


A​lternative water sources

Where mains water and other water sources, such as rainwater, recycled water, river water and borehole supplies, combine it is essential to notify the relevant water undertaker to ensure adequate backflow protection arrangements are installed.

Alternative water supplies should never be directly connected to the mains drinking water. The only legal and safe way to combine mains and another source of water is to use an arrangement called a break tank which enables separation of supplies. Typically, this is done using a Type AA or Type AB air gap the key features being:

  • An unrestricted or weir spill over
  • The pipework supplying the mains water must be external to the tank
  • The mains water feed must discharge at a higher level than and maintain a minimum clearance (twice the internal diameter (2D) of the supply pipework or 20 mm whichever is the greater) from those another sources
  • The water in the tank should not come into contact with the mains water inlet for example as a result of splashing.






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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.