Introduction to backflow prevention transcript
  • Last updated:
  • 21 Feb 2020

Hi we're here at Landers Shoot water treatment plant here on the Sunshine Coast.

Landers Shoot supplies the majority of drinking water for the Sunshine Coast region. At this plant raw water is put through a number of processes to remove any impurities or organisms that may cause sickness or disease.

We're lucky to live in a region where you can safely drink water from a tap. This is not the case in every part of the world.

Here at the water treatment plant a great deal of effort goes into making our water supply safe and backflow prevention is one of the methods that we use to keep it that way. Backflow prevention devices play an important role in protecting our drinking water supply from contamination, after it leaves the water treatment plant. Our drinking water is also used for washing, cooking, firefighting, commercial and industrial purposes where chemicals poisons bacteria and other contaminants may be used.

Properties also use water from tanks, bores and dams in addition to the main drinking water supply. These alternative water sources can be contaminated and for this reason they must be separated from our drinking water supply. These properties use backflow prevention devices to stop any contaminated waters from flowing back into the drinking water.

Backflow prevention devices are all around us, but you probably don't notice them. They are on your hosts tap to protect the water supply from whatever you might be washing out. They are built into household water meters to protect the mains water from activities on your property. There is even one in your toilet system to separate the draining system from the water supply.

These types of backflow prevention situations are a low hazard and can use non testable backflow prevention devices. As pollutants become more dangerous or the potential of contamination is more likely, we need to use more sophisticated devices.

The most common type of medium hazard device is a double check valve or a DCV. A DCV works by forcing the water past the first check valve, and builds up enough pressure to open the second check valve. Water can pass through the check valve. If the water flow reverses, the check valves will close preventing contamination from the drinking water supply.

Reduce pressure zone devices or RPZ are used for high hazard situations. RPZD incorporate a relief valve that is forced closed by the pressure of the water prior to the water being allowed to pass through the first check, and then the second check valve.

If the water supply reverses, or there is a back pressure situation, the second check valve will close reducing the pressure on the relief port, allowing it to open and drain the water from the relief port without contaminating the drinking water supply.

Any drop in pressure on the supply side or increase in pressure on the demand side, will trigger the relief valve to open, allowing water to discharge from the relief port and prevent contamination of our water supply. This is a signal that you may have a backflow issue.

Both medium and high hazard backflow prevention devices need regular testing to ensure they are working correctly. Testing involves checking the pressures in the chambers or zones of the valve, to ensure that the check valves are not leaking. Any valves that do not pass the test must be repaired or replaced immediately.

Owners of a testable backflow prevention device must have the device registered with local government and ensure that the valve is tested at least every 12 months.

The backflow prevention device needs to be an accessible location and vegetation must be kept clear of the device. Plumbers must be endorsed to carry out backflow prevention testing and provide council with the test results within two weeks of conducting the test. So please maintain regular testing so that together we can ensure the safety of our water supply. Factsheets about maintaining backflow prevention devices and owners responsibilities are available on council’s website.