Backflow is the unwanted reverse flow of water within a plumbing system that can result in contaminants being drawn into the water supply system.
The contaminated source can enter through a cross connection with the drinking water supply. The water supply system is designed to ensure that water flows to your property under pressure, but if this pressure is not maintained, there is a chance that water could be drawn back into the Metrowater supply system.
Causes of backflow
There are two basic causes of backflow.
- A sudden drop in mains pressure causes the water to siphon back into the system
- The water supply is directly connected to equipment, such as a boiler or a private bore, which is at a higher pressure than the water supply system, forcing water into the supply system.
Backflow is prevented by installing a backflow prevention device such as a one-way valve which prevents the contaminants from entering the potable water supply.
Responsibilities
It is the property owner’s responsibility to ensure that the correct boundary device is installed at their water connection(s).
Boundary devices must be tested annually and results submitted to Metrowater.
High risk properties must have their boundary devices tested annually by Metrowater. Non-compliant properties are automatically re-classifi ed as high risk. There is a charge associated with this annual testing,
Medium and low risk properties may be tested by an independently qualified person (IQP (backfl ow)) of the property owner’s choosing.
Property owners must maintain their boundary device(s). Metrowater reserves the right to rectify or upgrade a faulty device to reduce risks to the water network. Reasonable costs for this work will be recovered from the property owner.
What device do I install?
All water meters should have a device to prevent backflow, however the more dangerous the backflow the more complex the device that is needed. Properties are classified into three degrees of risk and this will determine the type of backflow device required.
- High Risk sites are properties that use or produce products of a toxic or bacterial nature that may cause death or serious illness if leaked into the main water supply.
Examples of high risk sites are hospitals, mortuaries, chemical plants, cooling towers, air conditioners and hairdressing salons.
Backflow device: Reduced pressure backflow device (must be tested annually).
- Medium Risk sites can endanger health if backflow occurs.
Examples of medium risk sites are public swimming pools and commercial laundries.
Backflow device: Double check valve backflow device (must be tested annually).
- Low Risk sites are properties that could cause a nuisance by colour, odour, or taste but do not endanger health.
An example is most residential homes.
Backflow device: Air gap separation or hose vacuum break valve (non-testable).
Brochure: Backflow Prevention - Protecting the Safety of Our Drinking Water
For further information please Contact Us.