How backflow happens
Water normally flows from the main into your property because the main is at higher pressure. If pressure in the main drops suddenly, for example when a main bursts or fire crews draw heavily on a hydrant, water can be sucked backwards out of your pipes. Plumbers call that back-siphonage.
The other way is back-pressure. If something on your side, such as a pump, pushes harder than the mains, it can force water back out into the supply. Either way, whatever is in your pipes, from garden fertiliser to process chemicals, could end up in other people's drinking water.
Where devices are found
Backflow devices sit where something other than clean drinking water is connected to the plumbing. They can turn up on irrigation systems, rainwater tank connections, fire services and commercial equipment. The QBCC's DIY guide in Queensland, for example, mentions irrigation fed from downstream of a backflow device.
If you are not sure what you have, a plumber can find it. If you have been sent a notice or reminder, keep it and have it ready for the plumber.
What happens at a test
Find and record the device
The plumber identifies the device type, size, make and serial number, and notes where it sits.
Turn the water off briefly
Testing usually means isolating the supply through the device, so let the people in the building know.
Test each valve
A test kit is connected to the device's test points, and each check valve or relief valve is checked against what it should hold.
Repair if it fails
Worn seals or springs are often replaced on the spot, then the device is tested again. A device beyond repair is replaced.
Report the result
The plumber gives you a record of the test and, where it is required, sends the result to whoever asked for it.
Your part and the plumber's
You can
- Find the device if you can, often near the water meter or at the start of an irrigation line, and keep the area clear.
- Keep every notice, test report and invoice together.
- Warn tenants, staff or neighbours on shared supplies that the water will be off for a short time.
- In Queensland, irrigation downstream of a tap, isolating valve or backflow device is on the QBCC guide's list of unregulated work. The device itself is not; for other states, see what you can do yourself.
Leave to a licensed plumber
- Testing the device.
- Repairs, parts and replacement.
- Installing a new device where one is needed.
- Lodging the test result or certificate where your state or water supplier requires it.
Rules and paperwork
Who must test, how often and where results go differ around Australia. We have not been able to confirm those rules for every state, so ask the plumber and whoever sent the notice. Two rules we have confirmed concern installing or changing a device.
In Western Australia, installing or replacing a backflow device is not minor work. The plumber gives notice at least 24 hours before starting and a certificate of compliance within 5 working days of finishing. In South Australia, backflow device work is listed among the work that needs an electronic certificate of compliance, provided to the customer within 7 days. See our compliance certificate guide for more.
Questions to ask the plumber
- Do you hold whatever licence or endorsement our state requires for backflow testing?
- Will you send the result where it needs to go, and give me a copy?
- If the device fails, can you repair it at the same visit?
- Is this device the right type for what is connected here?
- How long will the water be off?
What we would do
Do not let a test notice sit. Book it well before the due date so there is time to repair the device if it fails. Ask the plumber to confirm in writing that the result has been sent where it needs to go, and file the report with your property records. If several devices are on one site, have them all done at one visit. A plumber who does backflow work regularly will carry the test kit and common spare parts.