Backflow Prevention and Testing Adelaide: Annual Certification Done Properly

What backflow is, and why it is regulated at all

Water in a drinking supply is meant to travel one way. Backflow is when it travels the other way, out of a property and back into the main, carrying whatever it picked up on the way. It happens for 2 mechanical reasons and neither of them is exotic.

• Back siphonage: pressure in the main drops, usually because of a burst or a hydrant drawing hard nearby, and the resulting suction pulls water backwards out of connected properties.
• Back pressure: a system inside a property is at higher pressure than the main, from a pump, a boiler, a pressure vessel or simply a tall building, and it pushes its own water back out.

The reason it is regulated rather than left to good intentions is that the consequence lands on people who had nothing to do with it. A hose left in a chemical drum, a fertiliser injector on an irrigation line, or a dental chair with no separation can put contaminated water into a street main serving a whole neighbourhood. The device on your meter is not protecting you from the network. It is protecting the network from your property.

Which properties need a testable device

Hazard rating is what decides both whether a device is required and which one goes in. It is assessed on what is actually connected on the property and what would happen if that content reached the drinking supply, not on the type of business on the sign out the front. AS/NZS 3500.1 sets out the hazard ratings and the device selection that follows from them.

Containment protection is the layer that matters to the water authority. It is a device sitting immediately downstream of the water meter, protecting the main from the whole property in one go, and it is what SA Water is concerned with. Inside the boundary a property can also need zone protection, which isolates a wing or an area, and individual protection at the fixture itself. A site with an RPZD at the meter can still need separate protection at the hazard, and the 3 layers answer different questions.

What actually happens at an annual test

The test is a measurement, not an opinion. Calibrated gauges are connected to the test points on the device and its internal check valves and relief valve are put under differential pressure to see whether they hold to the figures the standard sets. The device either meets them or it does not.

1. The device is located and identified, along with its size, type, serial number and where it sits on the property. On a site nobody has tested for a while this is the step that takes the longest.
2. Water is isolated for a few minutes. On a commercial site that is worth planning around, so tell us what cannot be interrupted and when.
3. Calibrated gauges go on the test cocks and each check valve and the relief valve are tested in turn against the standard.
4. The readings are recorded on the Office of the Technical Regulator report form, along with the device details and the result.
5. Where the device fails, it gets rebuilt or replaced and then retested, because a failed test on its own leaves the property no better off than before.
6. The completed report is lodged with the Office of the Technical Regulator within 7 days, and you get your copy for the building file.

Test gauges themselves have to be kept in calibration, which is part of what separates a certified test from someone having a look at the device. A result from gauges out of calibration is not a result.

When a device fails, and what that costs you in disruption

Most failures are wear rather than catastrophe. Check valve seats and springs, the relief valve diaphragm, and debris off the main holding a seat open are the usual findings, and on almost every make the answer is a rebuild kit rather than a new device. A body that has cracked or corroded through is the exception rather than the rule.

• An RPZD discharging continuously from its relief valve is telling you something has failed inside it, and it will keep dumping water until it is repaired.
• An RPZD that discharges briefly when a nearby appliance starts or the main pressure fluctuates is doing exactly what it is designed to do. That is not a fault.
• A device that has been fitted below ground, or in a pit that floods, cannot be tested properly and is not compliant regardless of its condition.
• A device installed the wrong way round, or without the isolating valves and test cocks it needs, cannot be certified until that is corrected.
• A missing or unreadable serial number makes a device hard to record and hard to prove, and is worth fixing at the next test.

Where a device is genuinely at the end of its life, replacing it is planned work rather than an emergency, and it is worth doing at a time that suits the site rather than when the annual test forces the issue.

New installations and rectification work

Installing a containment device is licensed plumbing work and it needs to be done to the standard, with the right device for the hazard, the right isolating valves, accessible test cocks, and enough clearance to actually get gauges onto it. A device that cannot be reached cannot be tested, and a device that cannot be tested is not doing its job on paper even if it is doing it in the pipe.

• Selection to the hazard rating rather than to whatever was on the truck, because an underrated device is a compliance problem and an overrated one is money spent for nothing.
• Above ground, accessible, and clear enough around it to fit gauges and to rebuild it in place later.
• Protected from the weather and from vehicles where that is a real risk on the site.
• An RPZD needs somewhere for its relief discharge to go, which is a real design decision and not an afterthought.
• Commissioned, tested and reported at installation, so the property starts its 12 month cycle with a lodged certificate rather than a gap.

On a site with several devices, the practical thing is to bring them onto the same annual cycle so testing is 1 visit and 1 set of paperwork rather than a rolling series of separate ones through the year.

Questions we get asked