Backflow prevention

Keeping water free of contaminants

'Backflow' is water that flows backwards into our pipes after a property has used it. This water may carry contaminants that can harm people's health. That's why all connections to our water and recycled water pipes – including fire service connections – must be protected with devices for backflow prevention containment. Property owners are responsible for getting the right kind of backflow device installed.


What backflow is

Backflow occurs when water from a customer's property flows backwards into our pipes. This may carry contaminants that can harm people's health. Backflow is more likely to occur if:

  • there's a drop in pressure in the main, for example during a main break
  • water pressure at the property is higher than at the main, for example if a pump is operating on the site.

Contaminants may enter the drinking water system through a cross connection caused by:

  • faulty plumbing
  • hoses submerged in buckets, tanks or pools.

Cross connections are unauthorised plumbing connections between 2 water sources that should be separate, for example a drinking water system and a recycled water or wastewater system.

Contaminated water can pose serious risks 
Contaminants may include chemicals, oil, bacteria, mud and debris.


What backflow devices are

Backflow prevention devices stop water flowing back into our pipes. They have one of the following elements to stop water flowing backwards:

  • a valve that only lets water go in one direction
  • an air gap
  • a break tank.

These devices are important as they protect our water quality, and the health of people using it.


What you must do

Property owners are responsible for getting the right kind of backflow device installed. If you're the property owner, you need to ensure:

  • you have the right kind of backflow prevention device installed at your property
  • the device is properly maintained. 

Assess the hazard rating 

You must engage an accredited backflow plumber (a licensed plumber with a backflow accreditation) to assess your site's hazard rating. They need to assess the hazard rating every time site activities change. Tell them if your property has more than one connection to our water main. This may affect your hazard rating and the type of device the plumber must install.  

Install the device 

You must get a licensed plumber to install the right kind of device. You're responsible for ensuring your plumber sends us a certificate of compliance when they install high and medium hazard devices.

Test the device

Your accredited backflow plumber must test high and medium hazard devices when they're installed and every year afterwards.

Send us the results

Ensure your accredited backflow plumber sends us the results within 2 days of the test.


What type of backflow device you need

Your backflow device must be suitable for your property's hazard rating. A hazard rating measures whether your property is a high, medium or low hazard to our water supply system. Your accredited backflow plumber will assess your rating. Examples of hazard ratings for different businesses are shown in the Australian Standard, AS/NZS 3500:1.

Low hazard properties

Owners of low hazard properties must get a non-testable backflow prevention containment device installed. Our 20mm and 25mm meters have a simple backflow prevention device in them. These are suitable for low hazard connections.

You must get a separate device installed if you have:

  • a larger meter
  • an unmetered water connection
  • a high or medium hazard rating.

Medium hazard properties

Owners of medium hazard properties must get a testable double check valve assembly installed. 

High hazard properties

Owners of high hazard properties must get a registered break tank, reduced pressure zone or registered air gap installed.

Metered standpipes

If we've given you permission to use a metered standpipe on our pipes, your standpipe must have a testable double check valve incorporated into its design.

Construction sites

You need a backflow prevention device on water main connections you use for construction and renovation.

If you're building more than a single standalone house, we consider it to be a high backflow hazard.

Sprinkler and fire services

If your property has separate sprinkler and fire services, you must get a testable double check detector assembly. It must be installed near where the water service enters your property or upstream of any booster assembly or off-take from the fire service. 

If your property has a window or wall drencher system, you must install a non-testable low hazard device.

Unknown hazard rating

If you don't know your site's hazard rating or don't get it assessed, we'll assume it's a high hazard. Owners of properties with unknown hazard ratings must get a registered break tank, reduced pressure zone or registered air gap installed.


Who can fit your device

You must use accredited backflow plumbers and licensed plumbers. 

  • An accredited backflow plumber must assess your site's hazard rating and test your backflow device. Search for an accredited backflow plumber
  • licensed plumber must install your device. NSW Fair Trading licenses plumbers in NSW.

What we will do

We keep a register of all installed testable backflow prevention containment devices. We'll remind you when it's time to get your backflow device tested each year.

We audit a sample of installations to make sure they comply with Australian Standard AS/NZS 3500:1. If your installation doesn't comply with the standard, we'll send a notice asking you to repair, maintain, test or replace the device. 

If you don't comply with our backflow requirements or notices, we may:

  • restrict your water supply
  • disconnect you
  • charge you any costs we incur to make your connection satisfy our requirements.

Backflow prevention containment devices stop potentially contaminated water from flowing back into our water pipes.