Backflow is one of the biggest risks to our public water supply and can seriously affect the quality and safety of our drinking water.

Did you receive a letter from us about backflow prevention?

You may need to install a backflow prevention device at your property or let us know about an existing device.

Please complete our backflow prevention devices online form(external link) to:

  • let us know which installation option you’ve chosen, or
  • notify us of an existing device, or
  • get in touch with us.

We’ll email you back within 10 working days, usually sooner.

For more information about the consenting process, see Backflow prevention devices.

How backflow can happen


When the pressure drops in the public water supply and causes water to be sucked backwards from private property and into the public supply. Examples include large volumes of water being drawn for fire protection, during a water main or plumbing break, or during a shut-down of a water main or plumbing system for repair.


When water pressure from a private property exceeds the public water supply's pressure, causing water to be pushed into the public supply. Examples include when a tank is installed at a higher level than the public water supply, or a pump system is pumping at a greater pressure than that of the public water supply.

A serious risk

Because homes and businesses use chemicals and other potential contaminants, backflow can be a major threat to people's health and well-being.

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

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 prevention is assessed and identified according to the risk to the health of consumers.

In Christchurch City Council's 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 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 enough, especially if activities such as spa baths, swimming pools or dialysis machines exist within the premises. Protection within the premise must be carried out to comply with clause G12 of the New Zealand Building Code.

Hazard level Definitions Premises type Protection required What you can do
High Potential to cause loss of life

Commercial/industrial premises/zone 

(e.g. hairdressers, mortuaries, chemical manufacturing, dentists, drycleaners, medical facilities)

Reduced Pressure Zone Device or Registered Air-Gap

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

A building consent is required before installation can occur.

Medium Potential to cause illness

Residential premises

(e.g. swimming/spa pools, in-ground irrigation controllers, dialysis machine)

Testable Dual Check Device

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

A building consent is required before installation can occur.

Low Would cause a nuisance (by colour, odour or taste), but would not injure or endanger health


(e.g. fast-food drinks machines)

Testable 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, contact the Council or a plumber experienced in backflow prevention for advice.

Note: Water will not be provided until the backflow prevention device 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 Christchurch City Council for code compliance. 

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

Under current Local and Central Government legislation, backflow prevention 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.

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

A qualified person with plumbing certification must install backflow prevention devices and all testing of the device must be carried out by an Independent Qualified Person (IQP).

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

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 
  • The complexity of the installation