Backflow prevention

Council is implementing a backflow prevention device registration program across the Clarence Valley. This webpage sets out the obligations of Council and property owners with regard to backflow licensing requirements.

How does backflow occur?

The water supply system is designed to ensure your property is supplied with potable water under pressure. If there is a drop in the supply pressure, there is a risk that water could flow backwards into the water main. The water flowing back to the water mains could contain contaminates,  foreign matter, or debris. This usually occurs when there is cross-connection between potable and non-potable water sources. The contaminated water can then come out of the mains supply at another location, with the potential to harm.

Events leading to backflow:

  1. Water main pressure is reduced
  2.  A cross-connection between potable and non-potable water exists
  3.  Liquid metals/ chemicals/ waste/ debris enter potable water supply by either back-siphonage or back pressure
  4.  Another property uses the potable water supply.

Loss of pressure in the water supply could be as a result of:

  • A break in the water main
  • Mains water being used during fire fighting
  • A customer is using water at a higher pressure than that within the water mains
  • Constant back pressure caused by an outlet being higher than the water main.

Cross-connection between the water supply and a contaminated source could create a vacuum and therefore draw contaminated liquid back into the water supply. Some types of properties that pose a risk to the water supply are:

  • Chemical plants/ paint manufacturers and users
  • Light and heavy industry
  • Medical/ Dental/ Veterinary surgeries
  • Laundries
  • Nurseries/ market gardens
  • Golf courses/ sporting ovals/ caravan parks
  • Pest controllers
  • Grey water treatment systems – both domestic and commercial
  • Residential properties with rainwater storage plumbed into the house

Examples of how back-siphonage and back-pressure can occur:

Back-siphonage can occur when an inlet (e.g. shower hose) is submerged in bath water and the water is "sucked" into the mains supply due to a reduction in mains pressure. This would contaminate outlets in the house such as kitchen taps. This siphonage could also occur with an inlet being submerged in chemical containers, with the resulting siphonage contaminating the potable water supply.

Back-pressure occurs when the pressure within plant on a property exceeds that of the water supply mains. For example, a boiler that is chemically treated and has a higher discharge pressure than the mains supply can "force" the water back into the potable water supply, contaminating it with chemicals.

After a backflow incident occurs, dangerous contaminants may remain in the water supply. This contaminated water will flow to neighbouring properties when used for household purposes (such as drinking, showering, and washing) and could cause serious or fatal sickness and injuries.


Installation of a suitable backflow prevention device ensures that the potable drinking water supplied by Clarence Valley Council can not be contaminated by backflow due to a cross-connection. Most residential properties have a backflow prevention valve within the property water meter. This type of valve does not require annual testing due to the low risk of contamination to the water supply from normal residential use.

On properties that are assessed as a “high hazard” or “medium hazard”, the customer is responsible for the installation, on-going maintenance and annual certification of appropriate backflow prevention devices. Although you may already have backflow devices installed on your property, a backflow containment device is required regardless of any zone or individual protection devices.

Hazard Rating

A hazard rating on the processes carried out on your property will determine what type of device is required to be installed. There are three hazard ratings identified by AS/NZS 3500:1.

These are:

  • High hazard – any condition, device or practice which has potential to cause death when connected to the water supply.
  • Medium hazard – any condition, device or practice that could endanger health when connected to the water supply.
  • Low hazard – any condition, device or practice that would be a nuisance but does not endanger health when connected to the water system.

Due to processes and procedures differing within business types, consultation should be sought with an accredited backflow prevention plumber to establish which device is required for your property.

Annual Testing

Owners who have a testable backflow device installed are required to have it tested every 12 months. This includes the following devices: atmospheric vacuum breakers, double check valves, registered air gaps, registered break tanks and reduced pressure zone devices.

You will be advised by letter when the annual test is due. Testing ensures that the device is operating correctly. A defective device can:

  • Cause a backflow incident
  • Allow water through leaking devices
  • Cause a reduction in pressure on your property.

Annual testing must be carried out by a licensed plumber with backflow prevention accreditation. The licenced plumber will complete a backflow prevention device inspection test sheet for each device and provide a copy of these forms to you for your own records and for forwarding onto Clarence Valley Council within 10 working days of the certification testing being undertaken.

If the backflow prevention device fails the annual inspection, the plumber is obliged to conduct remedial action to ensure the safety of the water supply. Repairs and cleaning may resolve issues within the device, however if the device is faulty then the device must be repaired or replaced. The cost of this is the responsibility of the device owner.

If an owner does not have the device tested a reminder notice will be sent to the owner. If this is not acted on and Council does not receive the test result and fee, qualified Council staff will undertake the certification testing and charge the customer the appropriate testing fee as specified in Council’s Fees and Charges.

Annual Registration Fee

Clarence Valley Council has an annual registration fee per backflow prevention device. This fee covers the administration costs of implementing and maintaining Council’s backflow policy. The fee will be can be paid in cash, cheque, credit card or debit card (EFTPOS) at the Grafton or Maclean Clarence Valley Council customer service offices. Cheques are to be made out to Clarence Valley Council, and mailed to Locked Bag 23, Grafton, NSW, 2460.

What happens if I don’t install a device when required?

If you do not comply, Clarence Valley Council may disconnect the customer from the public water supply system until such time as the customer has complied with the notice and charge the appropriate fee in the fees and charges for disconnection/reconnection.

Further Information

Further information on backflow prevention devices can be obtained by contacting your local licenced plumber who is accredited in backflow devices, or the Clarence Valley Council Water Cycle Section on 02 6643 0200.

Document Downloads

  1. Council’s Backflow Prevention and Cross connection Control Policy”
  2. “Letter to Plumbers April 2015” – this letter was posted out to Clarence Valley plumbers in April 2015
  3. “Application for Sanitary plumbing and drainage” – this is the application form to be used when installing new devices.
  4. “NSW Government Test Book Order Form“ - this is the order form should plumbers prefer to purchase test books from the NSW Government instead of from Council
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