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Backflow prevention


Backflow is when there is an unplanned reversal in the direction of water flow in a pipe, and that flow then enters the public water network.  There is potential for any property to contaminate the water supply by backflow.

Could this be happening at your place?

Backflow can occur in two ways:

  • Back siphonage
  • Back pressure

Back siphonage is when water or another fluid is sucked back into the water supply when there is a drop in pressure in the water mains.  The most common cause of back siphonage at a home is the garden hose.  When it is left running underwater in a bucket or a swimming pool, it can take the water back into the water main.

Back pressure might happen when a fluid is pumped directly into the water main by a pressurised system.  This could be when a there is a cross-connection between a home owner's private garden irrigation system and the public water supply via the house pipes.

How to prevent backflow from happening

Devices can be installed to stop the flow of water back into the water supply.  It is the property owner's responsibility to pay for this backflow protection.  The type of backflow prevention device that needs to be used is based on the level of risk to the water supply from the property.

For homeowners, Ashburton District Council provides low level protection at the water connection to the public water supply.  This does not protect water from hazards that can occur within the home.

For some homes, such as where there is a swimming or spa pool, this may not be enough protection and another device may be needed.

For further advice on what type of backflow device you will need, please contact your plumber or Council on (03) 307 7700.