What Is Backflow Testing, Who Needs It in Sydney, and What Happens If You Skip It
Backflow is water running the wrong way: from your property back into the drinking water main, or from a hazardous fixture into your own taps. A backflow prevention device stops it, and if yours is a testable type, Sydney Water requires it to be tested every year by a licensed plumber with backflow accreditation.
The test takes 30 to 60 minutes per device with a calibrated gauge kit, ends with a tag on the device and a report to Sydney Water, and is quoted as a fixed price by the number of devices and how easy they are to reach.
What Backflow Is
Drinking water is meant to flow one way: from the main, through the meter, to your taps. Two things push it the other way.
Backpressure
Pressure on the property side rises above the supply pressure. A pump, a boiler, a heated system or a storage tank higher than the main can all push water back toward the meter.
Back-siphonage
Pressure in the main drops, during a burst, firefighting or heavy demand, and water is sucked back out of the property. A hose left in a pool, a trough or a chemical drum is drawn straight into the main.
Why It Matters
What comes back is whatever the water touched: cooling tower treatment, fertiliser, pool chemicals, wash-down water, sewage. Backflow prevention exists because those events have contaminated public supplies, which is why the rules are enforced rather than advisory.
Hazard Ratings and the Three Device Types
Australian Standard AS/NZS 3500.1 and the Plumbing Code of Australia rate every connection by what could come back, and match a device to the rating.
| Rating | What it means | Typical sites | Device |
|---|---|---|---|
| High | Backflow could cause death or serious illness | Medical and dental, laboratories, chemical dosing, cooling towers, sewage and recycled water, commercial car washes | Reduced pressure zone device (RPZ) or a registered air gap; testable |
| Medium | Backflow could cause illness or injury | Commercial kitchens, most commercial and industrial premises, fire services, irrigation with fertiliser injection, plumbed rainwater tanks, strata wash-down systems | Double check valve (DCV); testable |
| Low | Backflow would be a nuisance only | Standard houses, hose taps, domestic appliances | Dual check valve at the meter or a hose connection vacuum breaker; not testable, replaced when it fails |
Sydney Water assesses the containment rating for the whole property at the boundary, and individual fixtures inside can carry their own zone or individual protection on top. A cafe in a shopping strip is a common case: a medium-hazard containment device after the meter, plus individual protection on the dishwasher and any chemical dosing.
Who Has to Test, and How Often
The rule is simple once you know which device you have.
Testable Devices: Every Year
RPZ and double check valves must be tested when installed, after any repair, and then annually. Sydney Water requires the test to be done by a licensed plumber holding backflow prevention accreditation and the report to be lodged with them (Sydney Water backflow prevention requirements).
Non-Testable Devices: No Test
The dual check valve at a household meter and hose connection vacuum breakers are not tested. They are replaced when they fail or when the meter is changed.
Who This Usually Catches
Businesses of every size, strata and commercial buildings, fire sprinkler and hydrant services, schools and childcare, irrigation systems with dosing, anyone with a rainwater tank plumbed into the house supply, and pools with automatic top-up. Ask before assuming your house is exempt.
New Connections and Renovations
A new commercial fit-out, a rainwater connection or a change of use can move a property from low to medium hazard. The device is installed and tested before the connection is used, and the annual cycle starts from that test.
What the Test Involves
The visit is short. The paperwork is the part most owners never see.
Water is off to the device for the length of the test, typically 30 to 60 minutes, which for a building on a single containment device means a short planned outage. It is scheduled around trading hours.
- The plumber locates every device on the property and confirms its type, size and serial against the register.
- The device is isolated and a calibrated differential pressure test kit is connected to its test ports.
- Each check valve and, on an RPZ, the relief valve is tested against the pass values in the standard, and the readings recorded.
- A pass is tagged on the device with the date and the tester's details. A fail is repaired with a service kit or the device is replaced, then retested.
- The test report is lodged with Sydney Water and a copy given to you for your records. The next test is due in twelve months.
What Happens If You Skip It
The device does not stop working on the anniversary. The problem is that nobody knows whether it is working at all.
Compliance
Sydney Water follows up overdue tests and can take enforcement action on a property that stays non-compliant, up to restricting the supply for unresolved high-hazard cases (Sydney Water backflow prevention requirements). The council notices we see on jobs usually arrive with a deadline.
Liability
If a contamination event is traced to a property whose device was untested, the owner carries it. Insurers and body corporates ask for the test tags and reports.
The Device Itself
Check valves wear, springs weaken and debris jams seats. An untested RPZ that starts discharging from its relief port is often the first sign the owner gets, and by then it is a replacement rather than a service.
What It Costs and How We Quote It
This guide does not publish a price, because the price depends on how many devices you have, what type they are and how easy they are to reach.
- A single accessible double check valve on a shopfront is the quick end; a high-rise with an RPZ on the cooling tower, a fire service device and several zone valves is the long end.
- Every test is quoted as a fixed price before we attend, including the report lodgement with Sydney Water, so the number you approve is the number you pay.
- Repairs found during a test are quoted separately, on site, before they are done; a service kit is usually the answer for a device under ten years old.
- Put the next due date in your diary the day the tag goes on: the test is due twelve months from that date, and Sydney Water's follow-up is keyed to it.
Backflow Testing Questions, Answered
What is backflow testing?
A test of a backflow prevention device, an RPZ or a double check valve, with a calibrated gauge kit to prove its check valves and relief valve still stop water flowing back into the drinking supply. It is done by a licensed plumber with backflow accreditation, the device is tagged, and the report is lodged with Sydney Water.
Do I need backflow testing on my house?
Usually not. A standard house has a non-testable dual check valve at the meter. You need a testable device, and therefore an annual test, if the property has a plumbed rainwater tank, a pool with automatic top-up, an irrigation system with chemical dosing, a fire service, or is assessed medium or high hazard for another reason.
How often does a backflow device need to be tested in NSW?
Testable devices are tested when installed, after any repair, and every twelve months, with each report lodged with Sydney Water, under Sydney Water's backflow prevention requirements. Non-testable devices are not tested; they are replaced when they fail.
Who can test a backflow prevention device?
A licensed plumber who also holds backflow prevention accreditation and a calibrated test kit. The accreditation is separate from the plumbing licence; ask for it, the same way you would check the licence number.
What is the difference between an RPZ and a double check valve?
A double check valve has two check valves in series and is used for medium hazard. A reduced pressure zone device adds a relief valve between the two checks that discharges to atmosphere if either fails, which is why it is used for high hazard. Both are testable; a dual check valve at a house meter is a lighter, non-testable version for low hazard.
What happens if I do not get my backflow device tested?
Sydney Water follows up overdue tests and can take enforcement action against a property that stays non-compliant, up to restricting supply for unresolved high-hazard cases. You also carry the liability if an untested device fails and contaminates the supply, and the device wears unseen until it discharges or fails a later test.
How long does a backflow test take?
About 30 to 60 minutes per device, with the water off to that device for the duration. On a building with one containment device it is a short planned outage, scheduled around trading hours.
Related: Commercial plumbing · Strata plumbing · Water meter repairs · You or Sydney Water: who is responsible · How to check a plumber is licensed
