Backflow Prevention: Devices, Testing and Who Needs It

Backflow prevention is what stops water that has already left the main from finding its way back into it. Every property connected to Sydney Water’s supply has to have it in some form. For most houses that is a small device already built into the water meter. For a building with a fire service, a site with a second water supply, or a business that handles anything that shouldn’t end up in drinking water, it means a separate device that has to be tested every year.

This guide covers what backflow is, how a property gets its hazard rating, which device goes with which rating, and what the yearly test involves.

What is backflow?

Water in a supply pipe is meant to travel one way: from the main, through the meter and into your property. Backflow is when it goes the other way and takes whatever it has touched with it. Sydney Water’s own list of what can come back includes chemicals, oil, bacteria, mud and debris.

It happens in two ways.

• Back-siphonage. Pressure in the main drops, most often during a main break, and water is drawn backwards out of the properties connected to it.
• Back pressure. Something on the property pushes harder than the main does. A pump running on site is the usual cause.

Either way the water needs a path, and that path is called a cross connection: a link between drinking water and something that isn’t. Some are plumbing mistakes. Plenty are ordinary habits, like a hose left running with its end sitting in a bucket, a tank or a pool.

Who needs a backflow prevention device?

Every connection to the water main needs suitable backflow protection. What changes from one property to the next is the kind of device, and that depends on the hazard rating.

The hazard rating measures how much harm the property could do to the water supply if water flowed back out of it. There are three levels: low, medium and high. A licensed plumber assesses the site against the plumbing standard, AS/NZS 3500.1, and the rating has to be looked at again whenever what happens on the site changes. A tenancy that goes from one kind of business to another doesn’t automatically keep the rating it had.

If nobody has assessed a property, Sydney Water treats it as high hazard until somebody does.

Houses

A typical house on a standard meter is a low hazard connection, and Sydney Water’s 20 mm and 25 mm meters have a backflow device built in that suits it. If that describes your place, there is nothing extra to install and nothing to test.

A few things can change the picture at a house:

• Rainwater tanks. An above-ground tank is low hazard, and on a 20 mm or 25 mm meter it needs no extra device. A below-ground tank that collects rainwater only needs its own valve, a vented dual check valve.
• Greywater or stormwater reuse. Sydney Water rates alternative water supplies such as greywater and stormwater as high hazard.
• Building work. The water supply to a construction site needs a backflow device, and building anything more than a single standalone house counts as high hazard.

Businesses, strata and larger sites

Meters bigger than 25 mm have no device built in, so even a low hazard property on a larger meter needs a separate one. Medium and high hazard properties need a testable device. So does a fire service: sprinkler and fire hydrant services need a testable device on each connection, fitted close to where the service enters the property.

A property with more than one connection to the main needs a device on every one of them.

Which device goes with which rating?

Hazard rating	What Sydney Water asks for	Yearly test
Low	The device built into a 20 mm or 25 mm meter, or a separate non-testable device on a larger meter	No
Medium	A testable double check valve. On a fire service, a double check detector assembly	Yes
High	A reduced pressure zone device, a registered air gap or a registered break tank	Yes

These are containment devices. They sit at the boundary, just after the meter, and protect the public main from everything on the property.

Larger buildings often have a second layer inside: zone protection on one section of the plumbing, and individual protection on a single fixture or appliance. Those protect the people in the building from each other’s water. They are part of the building’s plumbing compliance, and they are not recorded on Sydney Water’s register.

How backflow testing works

A testable device has test points on its body so a plumber can connect a gauge kit and prove that each valve inside it is holding.

• The device is tested as soon as it’s installed, and every year after that.
• Medium and high hazard devices can only be commissioned and tested by a licensed plumber who also holds backflow accreditation. A plumbing licence on its own isn’t enough.
• The plumber lodges the result with Sydney Water within two days of the test. Ask for a copy of the report for your own records.
• Sydney Water keeps a register of testable devices and reminds the owner each year when the next test is due.

The water downstream of the device is off while it’s being tested, so on a business site it’s worth choosing the time. If the device fails, it’s repaired or replaced and then tested again.

What happens if it isn’t tested

The property owner is responsible for having the right device installed and keeping it maintained. That stays true when the site is leased.

Sydney Water audits a sample of installations. If one doesn’t comply, the owner gets a notice asking for the device to be repaired, maintained, tested or replaced. If the notice is ignored, Sydney Water can test the device itself and charge for it, restrict the water supply, or disconnect the property.

What you can do yourself, and what needs a plumber

You can:

• Keep hose ends out of buckets, ponds, pools and tanks while the tap is on
• Know where your device is, and keep the space around it clear so it can be reached
• Keep each test report and note when the next one is due
• Tell your plumber when the use of the site changes

Leave these to a licensed plumber:

• Working out the hazard rating
• Installing, moving or replacing a device
• The yearly test, which needs backflow accreditation as well as a licence

One small job worth knowing about at home: a garden tap can be fitted with a vacuum breaker, a simple device that stops water being drawn back up the hose. It’s the sort of thing we’d do alongside our tap and toilet repairs.

Getting a backflow device tested

We’re licensed plumbers with backflow prevention accreditation, based in Castle Hill, and backflow testing is one of the services we offer across the Hills District, Hornsby Shire and the Upper North Shore. If a test shows a device needs repair or replacement, you get a fixed price before any of that work starts.

If you’ve had a reminder or a notice from Sydney Water, or you’ve taken over a site and aren’t sure what’s installed, get in touch and tell us what the letter says. If you look after a building or a portfolio, our commercial and strata plumbing page explains how we work with managers and owners.