Plumbing rules in Sydney, a guide by DottoSix tags, from licence to label

Tag 05 · Backflow

Backflow prevention in Sydney: the device and the yearly test

A backflow prevention device stops used water on a property flowing backwards into Sydney Water’s pipes, where it could carry chemicals, oil, bacteria, mud and debris. Most stand-alone homes are covered by the device built into Sydney Water’s 20 mm and 25 mm meters; owners of commercial or industrial properties, and of any property with an on-site process, must have an accredited backflow plumber assess its hazard rating, or Sydney Water classifies it as high hazard.

General information, not technical advice. The official sources are Sydney Water’s backflow prevention page for property owners and Building Commission NSW’s note on cross connection and backflow control.

05-A · Who touches it

A device for accredited hands only

Not a do-it-yourself device

Only licensed plumbers with backflow accreditation from a registered training organisation may inspect, commission and test medium and high hazard backflow devices, and a licensed plumber must install the device. Sydney Water keeps a search of accredited backflow plumbers.

The household part is smaller. Sydney Water names two ways contaminants get into drinking water through a cross connection, an unauthorised link between water that should be kept apart: faulty plumbing, and hoses left submerged in buckets, tanks or pools. It also says backflow is more likely when the main loses pressure, during a main break for example, or when the pressure on a property is higher than in the main, such as while a pump is running.

05-B · Fire services

Sprinklers, hydrants and hose reels

For buildings with fire services, Sydney Water’s rules are specific:

Sprinkler or fire hydrant serviceOn each connection, a testable double check detector assembly, fitted near where the water service comes into the property and on the street side of any booster assembly or fire service off-take.
Upstream pipeworkNo galvanised pipes or fittings on the upstream side of the connection.
Window or wall drencherA non-testable low hazard device.
Fire hose reelBackflow containment protection, supplied from a Sydney Water metered service.
An older fire serviceSome have no device. If the service is moved, repaired, upgraded or redeveloped, it must be brought up to current requirements.

05-C · On the bill

The backflow fees on a Sydney Water bill

Only a property with a testable containment device pays these; a typical house does not.

Sydney Water’s residential pricing for 2026–27, as at October 2026.
ChargeWhen it applies2026–27
Backflow administration fee

Every quarter, one per property, toward Sydney Water’s backflow prevention program.

$11.05 a quarter

Annual test fee

If the yearly test is not done, Sydney Water may send an accredited plumber to test, charged for each device on the next bill.

$553.12 including GST

No access fee

If that plumber cannot test for reasons attributable to you, such as refused access or locked premises.

$431.68 including GST

One more thing the device changes: Sydney Water’s free repair of the pipe between its main and your meter does not cover a failure that relates to a backflow prevention device.

05-D · Inside the building

Specification 41, and where a device can sit

Inside the building, the Plumbing Code of Australia lists common hazard scenarios in its Specification 41, and each needs a device suited to its hazard rating. Where a hazard is not listed, the plumber either submits a Performance Solution or fits a default high hazard device such as a reduced pressure zone device, a registered break tank or a registered air gap. One NSW variation is about rainwater tanks: for a Class 1 building, drinking and non-drinking water must be zone protected from a rainwater tank with a non-testable device.

An isometric pipe run from the water main through a containment device at the boundary, a zone device in the building, and an individual device at one fixture M 1 2 3
Drawn for this guide, not to scale; the dashed line is the property boundary. M is Sydney Water’s main; 1, 2 and 3 are the three places a device can sit: at the boundary (containment), for a section of the building (zone), and at one fixture (individual). Sydney Water registers the boundary device, takes no test reports for the other two and sends questions about them to Building Commission NSW; its backflow page for plumbers has the definitions.

05-E · The yearly round

From the first assessment to the yearly reminder

  1. 1

    Assess

    An accredited backflow plumber works out the site’s hazard rating, and it is worked out again whenever what happens on the site changes. More than one connection to the main means more than one containment device. The device for each rating is set out on Sydney Water’s page.

  2. 2

    Install and register

    It falls to the owner to see that the plumber fits the right device, tests it and registers it. A newly fitted device is tested by a backflow-accredited plumber and registered straight away.

  3. 3

    Lodge the report

    The plumber has 2 days from the test to lodge the results. Ask for your own copy of the report.

  4. 4

    Every year

    Medium and high hazard devices are tested when they are fitted and then once a year. Sydney Water keeps a register of installed testable devices and reminds you when a test falls due.

Sydney Water also audits a sample of installations, and an owner who ignores its notices about a device that does not comply can face further action; its backflow page lists what it may do.