To ensure our water supply to the community remains safe and of high quality, the Christchurch City Council is committed to educating the community about backflow prevention devices and their responsibility to protect the public water supply.


One of the biggest risks to our water supply is backflow - caused when water pressure drops in the water distribution system causing water to flow in the opposite direction from residential or commercial premises back into the public water supply network.

Backflow occurs as a result of:

  1. Back-siphon - this can occur when the pressure drops in the town's mains and water flows from private property into the town’s mains.  A vacuum is created in the main and the water flows in the reverse direction.  Large volumes of water being drawn for fire protection; during a water main or plumbing system break; or during a shut-down of a water main or plumbing system for repair are examples of ways this can happen.
  2. Back-pressure - this can occur when the water supply pressure from a private premises exceeds the town’s mains supply and water is forced into the town’s mains.  Examples of this include: when a tank is installed at a higher level than the current water supply; or a pump system is pumping at a pressure which is greater than that of the town’s mains supply.

Because both homes and businesses use chemicals and other potential contaminants, backflow can be a major threat to the health and wellbeing of our residents and visitors.  

This risk needs to consider customers that consume water from the mains may be disabled or infirm, and for that reason the water quality should be to a minimum standard of the NZ Drinking Water Standards. 

At its worst, backflow contamination of the water supply could cause death or serious injury, so we all have a responsibility to help reduce this risk.

Preventing backflow

Backflow Preventer for high hazard protection

A typical Reduced Pressure Zone Backflow Preventer for high hazard protection

Homes and businesses use substances and liquids that could be a major threat to the health and wellbeing of our customers and visitors.  For that reason, backflow protection is assessed and identified according to the risk to the health of consumers.

In the Christchurch City Council district, the backflow risk arising from the activities on a premises is assessed and it is mandatory that an appropriate backflow prevention device is installed at the point of water supply.

All commercial and industrial properties are to have a minimum of medium hazard protection at the boundary to protect the main water supply.  The installation of this device is a condition of supply and is the responsibility of the property owner.

For homeowners, the Christchurch City Council provides low level protection at the point of connection to the public water supply.  It does not protect water from hazards that can occur within the home.

Sometimes the level of protection provided at the water connection may not be sufficient - especially if certain activities such as spa baths, swimming pools or dialysis machines exist within the premises.  Protection within the premise must be carried out under Section G12 of the New Zealand Building Act 2004.

Hazard level Definitions Premises type Protection required What you can do
High risk Potential to cause loss of life Commercial / Industrial premises Reduced Pressure Zone Device or Air-Gap

Contact a plumber experienced in backflow protection for advice and arrange an assessment and installation.

A Building Consent is required before installation can occur.

Medium risk Potential to cause illness Commercial / Industrial premises (minimum protection level for commercial / industrial premises) Testable Double Check Device

Contact a plumber experienced in backflow protection for advice and arrange for an assessment and installation. 

A Building Consent is required before installation can occur.

Low risk Potential to cause discomfort Domestic premises only Dual Check Device installed in the meter at the property boundary

The Council installs dual check devices at water supply connections to domestic premises. 

If you have areas within your premises that could cause risk to your drinking water (e.g. spa pool, dialysis machine), contact the Council or a plumber experienced in backflow protection for advice.

Note: Water will not be provided until the backflow preventer is installed and a commissioning test has been carried out.  The device must be certified by a suitably qualified person and a certificate must be sent to the Christchurch City Council for code compliance. 


New Zealand has strict legislation for the prevention of backflow to protect the safety of our water. The installation of backflow prevention devices is mandatory and is required in accordance with:

  • Christchurch City Council Water Supply, Wastewater and Stormwater Bylaw 2014
  • New Zealand Building Act 2004, Section G12
  • Health (Drinking Water) Amendment Act 2007
  • Drinking Water Standards for New Zealand 2005 (Revised 2008)
  • Ministry of Health Water Safety Plan Guide Ref: D2.4: Distribution System – Backflow Prevention
  • AS/NZS 2845.1 Backflow Prevention Water Supply Material Design Performance
  • AS/NZS 2845.3 Backflow Prevention Field Testing and Maintenance

Under current Local and Central Government legislation, backflow protection is required to be installed by the property owner and must be installed immediately when requested.

All annual checking of the operation and maintenance of any backflow prevention device is to be carried out by the property owner.

In our agreement to supply water through a water connection from the reticulated supply in Christchurch, all water connections are to be fitted with metering devices and backflow protection.

What you need to do

A building consent from the Council must be obtained before any medium or high backflow prevention device(s) are installed, refer Backflow prevention on devices.

A qualified person with Plumbing Certification must install backflow prevention devices and all testing of the device must be carried out by an Independently Qualified Person (IQP) on backflow.

IQPs are registered people who have been recognised as having achieved skills and experience in a particular field. See the South Island register below for a full list of registered contractors.

South Island register of IQP contractors(external link).

Backflow prevention devices have to be tested immediately after installation to attain code compliance for the building consent. Devices must then be tested annually to ensure they are working correctly and provide continuing protection.

Testing reports are to be retained by the owner and a copy is to be forwarded to Christchurch City Council to ensure the premise has a current Building Warrant of Fitness.

The property owner is responsible for the costs of installation, maintenance and testing of any backflow prevention device. Costs for installation will vary widely and depend on the:

  • Degree of protection required (risk level) 
  • Size of the device 
  • Complexity of the installation