Backflow Prevention and Annual Testing in Christchurch

What causes backflow

Backflow occurs either through back-pressure, where downstream pressure exceeds the supply pressure and pushes water backward, or back-siphonage, where a sudden drop in supply pressure, like a burst main or firefighting draw-off, creates a vacuum that sucks water back from wherever it can.

If a hose is left submerged in a trough, a chemical tank, or a pool, back-siphonage can pull that contaminated water straight into the drinking supply. This is exactly what backflow preventers are designed to stop.

Who typically needs a backflow preventer

• Commercial kitchens, cafes and restaurants
• Properties with a fire sprinkler system connected to the mains
• Irrigation systems, particularly with fertiliser or chemical injection
• Properties with a secondary water source, such as a bore or rainwater tank, connected alongside mains supply
• Medical, veterinary and laboratory premises
• Some multi-unit residential developments

Types of backflow preventers

The right device depends on the level of risk. Lower-risk situations might only need a simple check valve, while higher-risk connections, such as a fire system or chemical injection line, require a testable reduced pressure zone (RPZ) device that actively vents to atmosphere if it detects backflow.

Christchurch City Council's bylaw sets out which hazard rating applies to different property and connection types, and that rating determines the device required.

Annual testing requirements

Testable backflow devices need to be tested annually by a certified backflow tester, with the results submitted to Christchurch City Council. This isn't optional maintenance, it's a compliance requirement tied to the property's water connection.

The test checks that the internal components move and seal correctly under pressure. A device that looks fine externally can still fail internally, which is exactly why testing rather than visual inspection is required.

What happens if a device fails testing

• The device is repaired or replaced and retested before it's certified compliant
• Council may follow up if testing isn't completed within the required timeframe
• For commercial properties, ongoing non-compliance can affect trade waste or connection consents
• At property sale, an outstanding or failed backflow test is often flagged during due diligence

Keeping on top of it

We keep records of device location, type and last test date for clients, and can set up a reminder ahead of the annual due date so testing doesn't slip past unnoticed. If you're unsure whether your property has a device fitted or when it was last tested, that's worth checking sooner rather than later.

Frequently asked questions