Backflow Prevention

Backflow Prevention Management prevents water from ‘backfeeding’ into the water supply, contaminating the supply and potentially effecting the health of consumers. The types of backflow prevention devices required are stated in the NZ water guidelines and codes of practice. The higher the risk the premise poses to the water supply the stricter the controls. These control types will be checked during the inspections.

What is backflow?

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. Contaminants could be back-siphoned or injected by back-pressure into the public water supply.


A back-siphon occurs due to a loss of pressure in the public water distribution system. This can occur when large volumes of water are 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.

During a back-siphon, a reduction of pressure creates a vacuum in the piping and the water flows in the reverse direction. For example, if a hose tap is open when the end of the hose is submerged in a contaminated container of water, the contaminated water in the container can be siphoned into the premise’s plumbing.


Back-pressure occurs when water is being pumped at a pressure higher than the town mains or pressure within the building. When back-pressure occurs, water flows in the reverse direction to normal flow. It is important to understand that when coupled with a reduction in mains water pressure, the water source only needs to be slightly elevated above the public water supply pipe pressure to push the water back through the premises into the water mains.

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

How to prevent backflow

To protect our water supply, property owners have a responsibility to install devices and implement measures to stop the backflow of water into the public water supply. It is the owner’s responsibility to pay for backflow protection. This is in accordance with:

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.

To provide adequate protection, there are four levels of protection that should be provided according to the potential risk at the premises. Businesses, especially those that use chemicals, create a high risk to the water supply and therefore the need for backflow prevention is even greater.

Always call a qualified plumber to assist





High-risk situations:

  • Premises with an alternative non-potable water supply.
  • Premises where inspection is restricted.
  • Sanitary fixtures and systems.
  • Medical, dental, hospital, mortuary or veterinary equipment.
  • Piers, marinas, wharves and waterfront equipment and including ships’ water supplies.
  • Meatworks and abattoirs.
  • Sewage treatment plants.
  • Drainage systems.
  • Boilers.
  • Cooling towers and air conditioners.
  • Equipment, tanks, fixed hoses, hose attachment outlets, appliances and other forms of cross connection within:
    • car and plant washing facilities
    • dry-cleaning premises
    • photographic processing laboratories
    • funeral parlours
    • metal finishing plants
    • weed or pest spraying facilities
    • mixing of chemicals, pesticides
    • nurseries
    • chemical plants, any premises using, processing or manufacturing toxic chemicals
    • dental surgeries
    • chemical laboratories
    • pathology laboratories
    • universities and research facilities
    • timber treatment facilities
    • water treatment facilities
    • vehicular sewage disposal facilities.


Minimum recommended level of protection:
  • Reduced pressure backflow-prevention device.

     Air gaps provide a high level of protection, and are also an acceptable form of protection in these instances, so long as they are properly maintained.





Medium-risk situations:

  • Premises with alternative potable water supply.
  • Premises with grey water reuse systems, or where water is recycled for cooling or other purposes.
  • Premises with reticulated and disinfected water systems.
  • Public and private swimming pools, and spa pools.
  • Food and beverage processing plants.
  • Irrigation systems.
  • Commercial laundry facilities.
  • Premises with rainwater tanks.
  • Hairdressing premises.
  • Automatic fire sprinkler systems.
  • Equipment tanks, fixed hoses, hose attachment outlets, appliances and other forms of cross connection within industrial or commercial facilities where toxic or hazardous chemicals are not used.

Minimum recommended level of protection:

  • Reduced pressure backflow prevention device.
  • Testable double check valve.


Low-risk situations:

  • Premises used for the storage or preparation of food or beverages.
  • Drink dispensers.
  • Hose taps for fixed domestic irrigation systems.

Minimum recommended level of protection:

  • Testable double check valve.
  • 50mm Air gap.
  • Hose connector vacuum breaker (for hose taps).


Very low-risk situations:

  • All household units (ie, residences).

Minimum recommended level of protection.

  • Non-testable dual check valve (part of meter assembly maintained by water supplier).
  • 50mm Air gap.

Citation: Ministry of Health. 2014. Water Safety Plan Guide: Distribution System – Backflow Prevention

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 Hurunui District Council for code compliance.

What you need to do

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

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 on backflow.

Independently Qualified People are registered people who have been recognised as having achieved skills and experience in a particular field..

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 Hurunui District 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 they install. Costs for installation can vary widely and depend on the;

 backflow Prevention