What is Backflow

Properties are rated according to the level of risk they pose — either a low, medium or high hazard. These hazard levels are defined by two pieces of regulation: the Plumbing Code of Australia 2011 and the Australian/New Zealand Standard AS/NZS 3500. As advancements occur these regulations are amended according to increased responsibilities of both the property owner and the Network Utility Operator.

• Low: Risk of causing a nuisance.
• Medium: Risk of causing illness.
• High: Risk of causing death.

A cross connection occurs any time a property receives water from a potable supply — the user of the water and the provider of the water are connected. If a Backflow prevention device is not installed, or improperly installed, then contamination is a risk. Every property owner is thereby considered a risk and thereby susceptible to water shutoff if the legislated precautions are not taken.

Under normal conditions the pressure downstream of the cross connection is less than the upstream pressure. However, if this relationship is reversed backpressure occurs and contaminants may enter the potable water supply.

Back-siphonage, the other way backflow occurs, means just what its name implies — negative pressure in the main water line causes reverse siphonage to pull contaminates from the non potable water supply of a property into the potable water supply.

This policy is followed by all Network Utility Operators in Australia, it being their responsibility to ensure the safety of reticulated water supply systems for their designated areas. The user of these water supply systems has changed since this policy was first formed in 1995, and as these changes have occurred the policy has been amended.

For example, in 1996 hazard levels were introduced to the backflow containment policy. Whereas one risk level existed prior to this point, medium and high levels were subsequently added. Medium is regarded as a risk to health, while high is regarded as a risk of causing death, and low is simply seen as a nuisance.

Other issues resulting in amendment have included the use of alternative water supplies — such as industrial water and grey water — have placed strain on reticulated water systems due to containing chemicals and microorganisms. Another issue that required amendments was the use of recycled water, as opposed to drinking water, for non-consumption uses like washing cars and clothes, watering gardens and flushing toilets.

Listed below is legislation and regulation related to the Backflow Prevention Containment Policy.

• Plumbing Code of Australia 2011: This piece of legislation dictates how plumbing installations, like backflow preventers, are replaced, maintained, repaired and installed.
• Water Industry Regulations 2006: Property owner is responsible for testing and maintenance of the appropriate backflow prevention device.
• Safe Water Drinking Act 2003: This piece of legislation was ground-breaking in that it was the first time certain obligations of the type contained therein were applied to water suppliers — such as community consultation processes, information disclosure, standards for key water quality criteria and a risk management framework.
• AS/NZS 2845 Water Supply: Materials, design and performance requirements of backflow prevention devices are detailed in this legislation.
• AS/NZS 3500 Part 1: Property owners must pay for the backflow prevention device and its installation; also, the device must match the hazard rating for the property.
• Water Industry Act 1989 and 1994: The Network Utility Operator may disconnect the water supply from a property if the owner does not install, test, replace or maintain the appropriate backflow prevention device.