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Backflow prevention

Backflow is the term used for the unwanted flow of water in the reverse direction, back into the water supply system.

It can be a very serious health risk through contamination of drinking water and it can also be expensive to resolve. All connections to Council infrastructure must be carried out by a Council approved contractor.

What causes backflow?

Backflow is caused when water pressure drops in the water distribution system. This causes water from residential or commercial premises to flow in the opposite direction and back into the public water supply network. 

There are two basic causes of backflows:

Back-siphon

A sudden drop in mains pressure causes the water to siphon back into the system. This can occur when large volumes of water are being drawn for firefighting, or during a water main or plumbing system break; or during a shutdown of a water main for repair. The reduction of pressure creates a vacuum in the pipes and the water flows in the reverse direction. 

Back-pressure

Back-pressure occurs when the water supply is directly connected to equipment, such as a boiler or a private bore, which is at a higher pressure than the water supply system. This forces water to flow in the reverse direction and back into the system.

How to prevent backflow

Since 1997, all new properties in Tauranga must have a backflow prevention device fitted to their water supplies. Backflow manifolds have also been installed at other properties throughout the city, when new water meters have been installed or replaced. 

The installation of a backflow prevention device at the point of supply is a condition of supply and is to be fitted before the water supply connection is installed.

If other high risk hazards are identified, property owners will be advised that a greater level of protection is required.

Backflow prevention device definitions 

Level Definitions What you can do
Low level risk Has the potential to create discomfort due to changes in smell and taste. If you have areas within your premises that could create a risk to your drinking water, call the Council or your plumber* for advice. Your local hardware store or plumber’s merchant sells devices that can provide this level of protection e.g. hose pipe protection.
Medium level risk Has the potential to make people ill. Call your plumber* for advice and arrange for an assessment and installation of medium or high level protection.
High level risk Has the potential to cause loss of life Call your plumber* for advice and arrange for an assessment and installation of high level protection.

* Check your plumber has experience in backflow protection.

Tauranga City Council uses the following criteria to determine the level of backflow protection required for boundary protection and the acceptable solution for that risk.  It is an approved document from the Building Industry Authority for Water supplies, G12, Reprinted incorporating Amendments 1, 2 and 3.

Water Supplies Acceptable Solutions G12/AS1

Table 1: Selection of backflow prevention devices - Paragraph 3.3.1 and 3.3.2

Type of hazard

Acceptable devices

Relevant Standard or acceptable solution

High

Any condition, device or practice which, in connection with the potable water supply system, has the potential to cause death.

  1. Autoclaves and sterilisers
  2. Systems containing chemicals such as anti-freeze, anti-corrosion, biocides, or fungicides
  3. Beauty salon and hairdresser's sinks
  4. Boiler, chiller and cooling tower make-up water
  5. Car and factory washing facilities
  6. Chemical dispensers
  7. Chemical injectors
  8. Chlorinators
  9. Dental equipment
  10. Direct heat exchangers
  11. Fire sprinkler systems and fire hydrant systems that use toxic or hazardous water
  12. Hose taps associated with High hazard situations like mixing of pesticides
  13. Irrigation systems with chemicals
  14. Laboratories
  15. Mortuaries
  16. Pest control equipment
  17. Photography and X-ray machines
  18. Piers and docks
  19. Sewage pumps and sump ejectors
  20. Sluice sinks and bed pan washers
  21. Livestock water supply with added chemicals
  22. Veterinary equipment
Air gap

Reduced pressure zone device
G12/AS1 Figure 1

AS 2845:Pan 1
Note: The examples given are not an exhaustive list.  Where there is doubt comparison must be made to the hazard definition.

Medium

Any condition, device or practice which, in connection with the potable water supply system, has the potential to injure or endanger health.

  1. Appliances, vehicles or equipment
  2. Auxiliary water supplies such as pumped and non-pumped fire sprinkler secondary water
  3. Deionised water, reverse osmosis units and equipment cooling without chemicals
  4. Fire sprinkler systems and building hydrant systems
  5. Hose taps and fire hose reels associated with Medium hazard
  6. Irrigation systems with underground controllers
  7. Irrigation without chemicals
  8. Livestock water supply without added chemicals
  9. Untreated water storage tanks
  10. Water and steam cleaning
  11. Water for equipment cooling
  12. Drink dispensers with carbonators
  13. Swimming pools, spas and fountains.
Air gap

Reduced pressure zone device

Double check valve
G12/AS1 Figure 1

AS 2845:Part 1

AS 2845:Part 1
Note:  The examples given are not an exhaustive list.  Where there is doubt comparison must be made to the hazard definitions.

Low

  1. Hose tap used for fixed domestic irrigation systems
  2. Facilities used for the storage or preparation of food and beverages
Air gap

Reduced pressure zone device

Double check valve

Hose connection vacuum break
G12/AS1 Figure 1

AS 2845:Part 1

AS 2845:Part 1

AS 2845:Part 1

Source:  Building Industry Authority , October 2001

Table 2: Selection of Backflow Protection Paragraph 3.4.5

Type of backflown prevention

Cross Connection Hazard

 

HIGH

MEDIUM

LOW

  back -pressure back-siphonage back-pressure back-siphonage back-pressure back-siphonage

Air Gap

(Note 1)

X

X

X

X

X

X

Reduced pressure zone device

X

X

X

X

X

X

Double check valve assembly (Note 2)    

X

X

X

X

Pressure type vacuum breaker(Note 3)  

X

 

X

 

X

Atmospheric vacuum breaker(Note 4)  

X

 

X

 

X

  Note:

  1. Air gaps must not be installed in a toxic environment.
  2. Double check valves can be installed in a medium and low hazard toxic environment.
  3. Pressure type vacuum breakers are designed to vent at 7 kPa or less.  However, they require a significantly higher pressure to reseat and must be installed only in systems which provide pressures sufficient to ensure full closing of the valve.
  4. Hose outlet vacuum breakers are a specific type of atmospheric vacuum breaker.

Source:  Building Industry Authority, November 2004

 


Last Reviewed: 08/02/2018
 

 
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