Backflow Prevention

Back flow in Perth is a fairly new thing in the grand scheme of plumbing. There has only been back flow legislation in Western Australia for about 15 years, before that physical forms of backflow prevention was utilized (Break tanks, cisterns, physical air gaps between a contaminated and non contaminated source). At the moment Perth is still going through back flow hazard auditioning where the Water Corp backflow team inspects properties to work out if they need boundary protection and issue notices to be installed to the owner. Most commercial properties require a form of back flow prevention installed straight after the water meter for boundary protection (Protecting the mains water from anything inside the commercial premises) The installation of such valves protects people from the potential of contaminated / deadly water from entering the drinking water system. Water Corp Backflow.

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Backflow Device Hazard Levels

  • Low hazard: Vacuum breakers on outside taps, double check valves on some irrigation connections etc. The hazards are deemed to be a nuisance if anything, little chance to hurt or injure people.
  • Medium hazard: Testable vacuum breakers, double check valves, irrigation connections which have a lower ground level then a flood level, or injection of non-lethal pesticides.
  • High hazard: Testable reduced pressure zone devices and registered break tanks.

Backflow Testing Perth:

Testable backflow prevention devices at the property boundary (RPZD, Double check, RBT) must be installed on high or medium risk properties. These type of valves legally require testing at commissioning by a licensed plumbing contractor and to be submitted to the Water Corp, additionally testing is required after any maintenance and after every 12 months by a licensed plumbing contractor qualified to test the devices.

The annual testing requests are sent out by email or post, and give you a set time to get the valves checked – its a simple process and can be carried out quickly, with all paperwork and recipes submitted on the day for your records. Failure to maintain a backflow device will result in the serving of a non compliance notice to the property owner or occupier.

On property valves do not require paperwork to be submitted yearly to the Water Corp however do require yearly testing – If you have medium to high hazard valves installed on your premises a maintenance schedule should be in place to ensure the valves are operating at designed and no potential risk of cross contamination can occur. These type of valves have to be managed in house, as the water corp do not manage this.


Further more, sometimes valves can start leaking or not work properly – this will require maintenance and an overhaul kit is usually installed. If your RPZD valves are continuously dripping or dumping a lot of water on your fire service, water service or non potable service – you need to get this valve inspected and repaired. Usually something simple has happened, a valve has broken, dirt, grit and foreign debris has clogged up the valve, or the valve seat itself is damaged. This is usually why valves are installed in duplicate, so encase of maintenance the system can keep running as normal.

Backflow Devices:

A back flow prevention device is a plumbing apparatus that prevents water flowing though it in reverse, preventing any hazardous substances siphoning through the apparatus into the potable (drinking water) supply.

There are many different types of backflow prevention devices including vacuum breakers, dual checks, testable vacuum breakers, double checks, break tanks, registered break tanks and reduced pressure zone devices, each installed in different places.

  • You would find check valves installed on storage hot water systems – such as a duo valve (isolation / non return valve), non-return valve, swing check valve, spring check valve.
  • You would find dual check valves installed on irrigation connections, downstream of your water meter, before a water filter (as required in the AS3500) small Reverse Osmosis installations and other low hazard areas.
  • You would find a hose tap vacuum breaker on outsides and indoors taps, the hose tap vacuum breaker prevents siphoning of water through the hose in a low pressure situation – for example if a water main bursts causing negative pressure in the supply line, it would prevent the hose from sucking up whatever the end was left in – filling a pool is a good example.
  • Testable vacuum breakers would be found on irrigation connections with the injection of non-lethal herbicides or pesticides and other medium hazard installations.
  • A double check valve would be found on a fire service installation or main, you may also find a double check valve detector assembly which has a bypass valve and water meter attached to locate or identify water leaks in the fire service. You may also find double check valves supplying water to medium hazard areas. A double check valve is easy to identify by the three testable nipples and valves, usually on top or on the side of the valve.
  • A Reduced Pressure Zone Device is used for high hazard installations, it has two pressure zones, and when it detects a pressure drop that’s outside its differential pressure of the two springs, it releases water through a vent on the bottom, effectively preventing a backflow situation. You will find a RPZ valve on all incoming water supplies on new commercial buildings and subdivisions, on all grease trap installations, on any high hazard installations, such as print works, plating works, slaughter yards, industrial painting facilities, smelters, chemical plants, concrete plants and the like.
  • Three types of protection, boundary protection – which protects the mains water supply from being contaminated from water located on site. Zone Protection – which isolates a zone to a non-potable water system – which permits water to be used for process or the like, but unable to be used for drinking water. Signs and identification of the non-potable water must be clear and visible. Point of use protection – where the device is installed to protect one fixture or appliance – for example, a mechanical make up water tank may be isolated from the potable water system, by installing an RPZ to protect the potable water system.


Back flow prevention Price
Annual testing (Water and Fire) $145 - $175
Additional valves $80 each
Servicing of back-flow valves $145 for the first hour excluding spares
Installation of new back flow valves POA

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