Within a water distribution system, circumstances can occur where backflow results in drinking water becoming contaminated. Water suppliers have an obligation to ensure that the actions of any one customer do not have an adverse effect upon others through the contamination of water supplies. The water supplier must therefore have clear policies on backflow prevention at the boundary1 between the water mains or aquifers and customers’ plumbing systems.
Backflow can occur when the pressure in a customer’s system exceeds the pressure in the supply system, either because of increased pressure in the customer’s system or reduced pressure in the supply system, for example due to a mains break or pump failure.
This document provides best practice guidance on how water suppliers can minimise the risk of backflow through the development of policies and practices covering the selection, installation and monitoring of backflow devices for all connections supplied with drinking water, including residential properties. This document is a revision of an earlier (2006) version that has been updated in response to changes in legislation, in particular sections of the Health (Drinking Water) Amendment Act 2007 that specifically refer to protecting water supplies from risk of backflow. Also, particular attention has been paid in this document to fire protection systems following consultation with representatives of the fire industry.