Backflow prevention

Backflow happens when dirty water or other liquids flow back into the clean water supply. You can avoid it with a backflow preventer.

Level of compliance Main audience Other


  • Boards
  • Principals and Tumuaki
  • Proprietors
  • Property Manager

Information about backflow and advice on where issues may occur. Learn about backflow preventers and how to pay for their installation and maintenance. 

Your health and safety responsibilities

Providing clean water at your school is part of your overall health and safety responsibilities. We recommend you review your school’s health and safety systems.

This will help you meet the requirements of the Health and Safety at Work Act 2015 — NZ Legislation website(external link)

Causes of backflow

Backflow happens when dirty water or other liquids flow back into the clean water supply. Its cause can be either:

  • back syphonage, when water pressure drops suddenly, creating a vacuum or partial vacuum in water supply pipes and sucks contaminated water into the water supply, or
  • back pressure, when the water supply is directly connected to equipment at a higher pressure, such as a boiler or a private bore, which forces water into the supply system.

Areas to watch for in your school

Your school may have backflow problems in:

  • science laboratories
  • dental clinics
  • boiler make-up water
  • fire sprinkler systems
  • untreated water storage tanks
  • swimming pools.

Backflow can contaminate school drinking water. It's a risk whether you use the town water supply or have your own water supply. You must manage this potential hazard.

Visit our Drinking water in schools webpage to find out more about drinking water in schools that use the town supply, and self-supplying schools.

How to deal with backflow

If you identify a backflow hazard at your school or think you might have one, seek expert advice from:

  • your local council building inspection team
  • a plumber, or
  • an engineer.

You'll probably need to install an appropriate backflow preventer or air gap system. This device stops the water from flowing backwards. It can be fitted:

  • at the point of possible contamination, or
  • to the water supply.

Requirements for installing a backflow preventer

If you're installing a backflow preventer as part of new work on an existing school building or in a new school building, you must follow the Building Code (G12 Compliance document).

If you're installing a backflow preventer in any other circumstances, we recommend you still comply with the Building Code requirements. In this way, you can manage any risk.

Backflow preventer at the school boundary

Some councils direct schools to install backflow preventers at the school boundary. Their aim is to protect the town water supply from backflow and cross-contamination. Such requests can be enforced legally.

If your local council directs you to install a backflow preventer at the school boundary, you should first:

  • contact your property advisor to get their confirmation and approval to go ahead with the installation
  • get advice about the most suitable and cost-effective ways to prevent backflow
  • get a suitably qualified person (such as an engineer or the drinking water assessor from your district health board) to check that the council’s assessment of the risk of contamination is valid.

Paying for a backflow preventer

Use your Five Year Agreement (5YA) funding to buy and install a backflow preventer. If you don't have the funds in your 5YA funding, contact your property advisor for advice.

Maintaining backflow preventers

Use your Property Maintenance Grant funding to pay maintenance costs for a backflow preventer.

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