Find out about:

• requirements
• backflow
• responsibility for backflow prevention
• minimising backflow risks in housing
• backflow prevention.

Requirements

The cold water supply to an occupied building must:

• include a potable (drinkable) water supply
• provide an adequate water flow rate to every sanitary fixture
• protect the source from contamination by cross-connection and backflow.

Backflow

Backflow is the unplanned reversal of flow of water, or a mixture of water and contaminants, into the water supply system.

For backflow to occur, there must be a physical connection, or cross-connection, between the water supply and any delivered water or contaminant. A common situation is the end of a garden hose submerged in a bucket or other container of liquid.

Backflow is caused by a difference in pressure and may occur due to:

• backsiphonage – the supply pressure is less than the downstream pressure allowing water to be pushed in the wrong direction
• backpressure – the downstream pressure is higher than the supply pressure causing water to travel in wrong direction.

Backflow of contaminated water (or any other substance) into the main supply of water must be prevented.

Cross-connections can occur in any situation where fixtures are connected directly to the main supply such as:

• irrigation systems
• dishwashers
• washing machines
• coffee machines
• swimming pools, spa pools or ornamental pools that are filled by hose
• water softeners
• pesticide and fertiliser attachments for hoses
• fridges and icemakers
• bidets
• retractable spray outlets to tubs and sink
• flexible shower hoses
• storage tanks.

Responsibility for backflow prevention

This may rest with:

• the network utility provider who may install a backflow prevention device as part of the meter assembly, or
• the individual property owner whose responsibility it is to comply with the requirements of the network utility provider and the Building Code, and to protect users within the premises.

Minimising backflow risks in housing

• Maintain an air gap in water supply tanks.
• Incorporate an air gap or means of preventing backflow for all appliances and fixtures directly connected to the water supply.
• Incorporate a hose connection vacuum break device to hose taps.
• Provide a dedicated water supply with an approved air gap to swimming and spa pools.

Advise building owners that they should:

• not leave garden sprayers connected to hoses
• always turn off the supply at the tap when not in use
• not submerge the spray head of a laundry tub, kitchen sink or shower
• not submerge the end of a garden hose in a pond, trough, or drain.

More information

•    www.moh.govt.nz/water
•    www.drinkingwater.co.nz
•    www.sustainability.govt.nz/water/water-supply
•    www.mfe.govt.nz/issues/water
•    www.waternz.org.nz
•    www.waitakere.govt.nz/AbtCnl/to/ecowtr.asp