Backflow Prevention


General Information




Important Definitions


Backflow - The unwanted reverse flow of liquid in a piping system.

Back pressure - An increase in the downstream pressure creating a reversal of the normal direction of flow.

Back siphonage- Backflow caused by a drop in supply pressure creating a negative pressure in the water system.

Cross connection- Any actual or potential connection between a water supply installation and a source of actual or potential contamination or pollution.

Potable water- Water that is suitable for human consumption.


Protection of safe water


Water authorities have a responsibility to provide safe drinking water from the point of treatment to the point of use. It is the property owner's responsibility to ensure that they do not affect the mains supply with any water from their property. (Unsafe water is called non-potable).


Backflow preventers are required by Australian Standards, National Plumbing and Drainage Code (AS 3500.1) for protection and conservation of safe drinking water.


Hazard rating


Any property that potable water enters is designated to be either a high, medium or low hazard area. These ratings are defined in AS3500.1 as follows:


  • High:   Any condition, device or practice within the water supply system and its operation which has the potential to cause death.
  • Medium:   Any condition, device or practice within the water supply system and its operation which could endanger health.
  • Low:    Any condition, device or practice within the water supply system and its operation which would constitute a nuisance but not endanger health.


Hazard Ratings determine the type of backflow prevention device that is required.


Who is responsible?


Manufacturers are responsible for providing valves which will meet the requirements of Australian Standard AS2845.1


Suppliers should be fully conversant with the units they are selling, and only sell valves that are approved by the relevant authorities for use in their intended application.


System designers of buildings should have up-to-date information on valves approved for use, installation criteria and the requirements of applicable codes.  System designers should get advice from local or regional authorities as to whether the proposed system will require approval prior to the system's connection to their reticulation system.


Plumbers must hold an endorsed registration in Water Supply Plumbing and be conversant with the devices to be installed and able to interpret relevant codes and standards for installation.


Owners / occupiers of buildings with backflow prevention devices must: make sure only approved valves are installed; make sure that there is ongoing maintenance, servicing and testing of installations; and use only competent and endorsed water supply plumbers to test and maintain valves.


Testers must: hold an endorsement in backflow device testing from the Plumbers Industry Board; be conversant with all devices installed and able to interpret all relevant codes and standards for installation, testing and maintenance; be able to give advice about device suitability; and be aware of the legal responsibilities of the tester.

Back to top

Back to Backflow Prevention