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Backflow

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What is backflow?

Backflow occurs when water flows in the opposite direction to its normal or intended direction. This unwanted reverse flow of water within a plumbing system can result in contaminants being drawn into the water supply system affecting the quality of our drinking water.  

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 Watercare 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.   

Backflow causes 

There are two basic causes of backflow.

  1. A sudden drop in pipe pressure causes the water to siphon back into the system.

  2. 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 devices 

Property owners must maintain their boundary device(s). Watercare 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.

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

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 include hospitals, mortuaries, chemical plants, cooling towers, air conditioners and hairdressing salons.

Backflow device: Reduced pressure backflow device (must be tested annually).

Medium Risk

Properties that can endanger health if backflow occurs. Examples of medium risk sites include public swimming pools and commercial laundries.

Backflow device: Double check valve backflow device (must be tested annually).

Low Risk

Properties that could cause a nuisance by colour, odour, or taste but do not endanger health. Most residential homes are low risk sites.

Backflow device: Air gap separation or hose vacuum break valve (non-testable).

To assess the risk for your property, please complete the Water Use Survey and forward to backflow@water.co.nz  

Backflow 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 Watercare.

  • All properties (high, medium and low risk) may be tested by an independently qualified person of the property owner’s choosing. Alternatively, a request can be made to Watercare to test the device at the published charges.  

  • Non-compliant devices (either failed or not tested on time) are automatically classified as high priority. Should these devices not be repaired and re-tested within a week of such non-compliance being notified, they may be tested by Watercare. There is a charge associated with this testing or repair (if required).