A backflow is the unwanted and undesirable flow of non-potable water or other liquids back into the water supply system from a consumer's premises.

There are two basic causes of backflows. They happen when...

1. Sudden drop in mains pressure causes the water to siphon back into the system
2. 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, forcing water into the supply system.
3. A break in the main is the simplest cause of liquids siphoning back into the water supply system. The break sets up a vacuum or partial vacuum in the pipes, sucking liquids in. The same effect can be produced by heavy demand from fire fighting or from flushing the pipes.

There are a surprisingly wide range of direct connections to the water supply system from which liquids can be drawn into the water supply system.

These include:

• air conditioners
• boilers
• cooling systems
• dishwashers
• hospital equipment
• laboratory equipment
• swimming pools
• private bores
• washing machines
• Vet Clinics
• Mortuaries

Besides these there are a range of fixtures with submerged inlets and the temporary connection of sprays, tanks, and pools and fish ponds.

Below is a backflow manifold similar to those that have been installed since 1997 to new connections. Every connection in the City has now been fitted with these devices. This device is suitable to protect against a "Low Hazard".

Backflow prevention manifold:

The Risks of Backflow

It is all well and good to treat water to the highest standard at the treatment plant, but it could all be to no avail if it gets contaminated in the pipes which carry it to your home.

Yet that is the risk. Sometimes water can flow into, rather than out of, the tap.

These "backflows" may not happen very often, but when they do, they can be serious. In one case in the United States, a contractor had a hose in a barrel of insecticide. This got sucked into the water supply and did US$40 million worth of damage to the supply system, and household appliances.

Fortunately in that case, nobody got sick. But one of the risks with back-flow is that someone will drink contaminated water.

Since 1997, all new properties in Tauranga have had to have a backflow prevention device fitted to their water supplies. Now, backflow manifolds have been fitted to all the other properties in the city at the same time as the new water meters are installed or replaced. Other higher hazards are identified through City-wide Surveys and in required, property owners will be advised that a higher level of protection is required