What is Backflow

What is Backflow?

Water supply, from the town mains into your property is normally maintained at an appropriate pressure so water can flow consistently from the tap, shower or other fixture.

This normal water pressure is reduced when a water main bursts or there is a high demand on the water system (for example, when several fire hydrants are opened).
Less pressure in the town mains pipe may allow contaminated water from your property to be drawn back into the main water supply system.This is called “backflow”. Water authorities require the mains supply be protected against backflow.

Back flow can be caused by the following events:

Pressure is reduced in the water main

The water supply system is designed to ensure that water flows to your property under pressure. If this pressure is not maintained, there is a chance that water could be drawn back into the Town water supply system. Water pressure can be affected when:

• there is a break in the water main
• water is being pumped from the main water supply during a fire
• a customer is using water at a higher pressure than the pressure supplied by the water authority
• heavy water use on site reduces water pressure within the supply network
• the water outlet on the property is higher than the water main.

Cross connection between the drinking water supply and a contaminated source:

There is a risk to public health if there is a cross connection between your water supply and a contaminated source. If there is a drop in pressure in the water main, a vacuum could be created in the water supply system. Under certain conditions this draws liquid from a potentially contaminated source back into the drinking water supply. Some examples of cross connections where a backflow incident can occur are:

• in metal processing or chemical plants chemicals used for production can come into contact with the water supply
• in market gardens, where chemical injectors, irrigation systems and garden hoses are connected to the water supply
• when a hose is left running in a container with chemicals such as fertilisers
• car wash facilities, where there is a connection between the scrubber and rinse cycles
• pipe work that allows recycled water to enter the drinking water supply.

Note that backflow prevention applies to town mains supply only. Always check with your local authority as to their requirements before installing any fertigation equipment.