Backflow: Overview

What is a backflow prevention arrangement or device?

It is in effect a barrier intended to prevent contaminated fluid flowing backwards.


Schedule 2 paragraph 15 of the water fittings regulations in England, Wales and Northern Ireland, byelaws in Scotland require every plumbing system to incorporate protection against backflow. This is often referred to as point of use backflow protection. It can be provided by an air or tap gap arrangement or a mechanical backflow prevention device. 

Backflow prevention arrangements and devices permitted under the regulations/byelaws need to be approved by the regulator  or alternatively authorised as a relaxation. Relaxations allow a water undertaker the discretion to accept an arrangement as preventing backflow. 

The regulator rates a backflow protection arrangement or device for suitability against contamination risk (fluid categories) and types of backflow risk - back siphonage or back pressure.

Backflow prevention devices, are required to be corrosion resistant. For example, for metallic backflow prevention devices manufactured of gunmetal or other dezincification resistant materials. Dezincification water fittings are typically marked with a CR symbol.

Wherever practicable plumbing systems should be protected against backflow without the necessity to rely on mechanical backflow protection devices.



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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.