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.
- Autoclaves and sterilisers
- Systems containing chemicals such as anti-freeze, anti-corrosion, biocides, or fungicides
- Beauty salon and hairdresser's sinks
- Boiler, chiller and cooling tower make-up water
- Car and factory washing facilities
- Chemical dispensers
- Chemical injectors
- Chlorinators
- Dental equipment
- Direct heat exchangers
- Fire sprinkler systems and fire hydrant systems that use toxic or hazardous water
- Hose taps associated with High hazard situations like mixing of pesticides
- Irrigation systems with chemicals
- Laboratories
- Mortuaries
- Pest control equipment
- Photography and X-ray machines
- Piers and docks
- Sewage pumps and sump ejectors
- Sluice sinks and bed pan washers
- Livestock water supply with added chemicals
- 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.
- Appliances, vehicles or equipment
- Auxiliary water supplies such as pumped and non-pumped fire sprinkler secondary water
- Deionised water, reverse osmosis units and equipment cooling without chemicals
- Fire sprinkler systems and building hydrant systems
- Hose taps and fire hose reels associated with Medium hazard
- Irrigation systems with underground controllers
- Irrigation without chemicals
- Livestock water supply without added chemicals
- Untreated water storage tanks
- Water and steam cleaning
- Water for equipment cooling
- Drink dispensers with carbonators
- 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
- Hose tap used for fixed domestic irrigation systems
- 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:
- Air gaps must not be installed in a toxic environment.
- Double check valves can be installed in a medium and low hazard toxic environment.
- 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.
- Hose outlet vacuum breakers are a specific type of atmospheric vacuum breaker.
|
Source: Building Industry Authority, November 2004
Last Reviewed: 14/04/2020