Preventing backflow

Make sure you’re not at risk of contaminating the water supply by taking steps to prevent backflow. Backflow is when anything flows back into the public drinking water supply, causing it to become contaminated. This can happen as a result of either ‘back-siphonage’ or ‘back-pressure’.

If backflow occurs due to back-siphonage or back-pressure into the public water supply, this can cause sickness, or even death.

Under Council’s Water Supply Bylaw, all consumers on the water supply must take steps to prevent backflow.

There are three ways of reducing the risk of backflow:

Point of supply - Restricted flow supply typical tank connection

  1. Maintaining an air gap between the tap or hose outlet and an external liquid
  2. For restricted supplies - having an overflow below the supply pipe inlet to the tank that is 2x the diameter of the supply, so backflow prevention is by way of an air gap (see diagram on right)
  3. Installing a backflow device - eg a ‘manifold’

Preventing backflow from domestic properties

Over the last few years, Council has installed manifolds (a simple backflow device) on the majority of taps on urban residential properties in Oamaru to help reduce the risk of backflow.

On any domestic property where a manifold isn’t installed, there is a risk of backflow whenever a tap or hose is submerged into liquid – for example, when filling a gardening spray pack.

If you don’t have a manifold or other backflow device installed, the easiest way to prevent backflow is to ensure you maintain an air gap at all times between the tap or hose and the external liquid.

If you use the outside tap to fill a swimming pool or spa pool, or use the tap to fill or wash chemical containers, then a manifold is essential. Please contact us if you require assistance with this.


Preventing backflow from businesses

Some businesses are at higher risk of contaminating the water supply through backflow. If your business is at risk of causing contamination through backflow, you must have backflow prevention device installed at the property boundary. The backflow device stops contaminants from your property entering the water network (please note, that this won't protect the occupants within the business premises). Once installed, the Council will inspect, maintain and replace the backflow device, as required.

Annual inspection and testing of the backflow device will be arranged by Council, and the cost of this will be charged to the property owner. If you have any questions about backflow devices, contact us on 03 433 0300.

Preventing backflow within a business premises

A boundary backflow device will not protect the water supply used within the business itself. This can only be done through ‘internal source protection’, which is when a backflow device is installed at the source of potential contamination.

Source protection is a requirement under the Building Act 2004 for all commercial buildings. The cost of installing and maintaining source protection is the responsibility of the property owner.