Backflow Prevention Devices and Annual Testing

What the device does

A backflow prevention device is a one-way valve between a property and the drinking water main. Under normal conditions water flows in and nothing happens. If pressure in the main drops below pressure on the property side — during a burst, a shutdown, or heavy firefighting draw nearby — water can be siphoned backwards. The device closes and stops it.

That matters because of what might be on the property side of the connection. Irrigation systems with fertiliser or chemical injection. Commercial process water. Fire services with stagnant water sitting in charged lines. Car wash and workshop equipment. Medical and dental suction equipment. None of that should ever reach the street main.

Who needs one

Ordinary suburban houses are generally covered by the individual protection built into fixtures — the air gap at a basin, the check valve in a washing machine inlet, the vacuum breaker on a hose tap. A separate testable containment device at the boundary is normally required where a recognised hazard is connected.

In practice that means commercial and industrial premises, food businesses, medical and dental practices, car washes and workshops, properties with a fire service connection, and irrigation systems that inject anything into the water stream. Reticulation drawing from a bore rather than scheme water raises its own cross-connection questions.

If you are not sure whether your property has one, look in or near the meter enclosure at the front boundary for a brass assembly with test cocks — small ports with screwed caps on the body of the valve. Those test ports are what distinguishes a testable device from a plain check valve.

Annual testing

Testable devices have to be tested at least once a year by an accredited tester, and the result submitted to the water service provider. The test itself is short: the device is isolated, gauges are connected to the test cocks, and the valve's ability to hold against reverse pressure is measured against the required differential.

It either passes or it does not. Common failures are debris sitting on a check seat, a perished relief valve diaphragm, or a spring that has lost tension. Most are fixed with a manufacturer's service kit on the spot, then retested.

The obligation attaches to the property. Buying a commercial premises with a device on it means inheriting the annual test, whether or not anyone mentioned it at settlement.

Where it fits alongside the rest

Backflow devices sit at the boundary, close to the meter, which is the same area involved when we are checking for a leak or dealing with a service line failure. If someone is already there, it is a sensible time to confirm the device exists, is the right type, and is current on its testing.

For everything else on a commercial or residential property, see the full services list or the general plumbing page.