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What is backflow?

Water flow into your property is normally maintained at a consistent 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 high demand on the water system (for example, when several fire hydrants are opened). Less pressure in the pipe may allow contaminated water from your property to be drawn back into the main water supply system. This is called backflow.

Backflow can be caused by the following events:

1. 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 Yarra Valley Water’s 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 Yarra Valley Water
  • heavy water use on site reduces water pressure within Yarra Valley Water’s supply network
  • the water outlet on the property is higher than the water main. 

2. If there is a 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 where metals in solutions or 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. 

Cross-connections can occur in a number of industries, such as chemical and metal processing plants, as well as in market gardens and nurseries, laundries, sporting ovals, and caravan parks.

3. A nearby property uses the water supply 

A dangerous chemical (or contaminant) may get into the water mains which leads into a nearby property. If this contaminated water is used, the occupants of the property could be seriously or fatally injured. 

More information