Backflow Prevention

Backflow is a term in plumbing for an unwanted flow of water in the reverse direction. It can be a serious health risk for the contamination of drinking water supplies with contaminated water. In the most obvious case, a toilet flush cistern and its water supply must be isolated from the toilet bowl. For this reason, building codes mandate a series of measures and backflow prevention devices to prevent backflow.

Backflow occurs for one of two reasons, either:

  1. Back pressure which is the result of a higher pressure in the system than in its supply, i.e. the system pressure has been increased by some means. This usually occurs in unvented heating systems, where thermal expansion increases the pressure.
  2. Back siphonage is the result of supply pressure being lowered below that of the system. This occurs when a supply is interrupted or drained down.

Backflow occurs when reticulated water entering a customer's property flows backwards into Councils reticulated water supply network. This may carry contaminants that can harm people's health as well as Councils infrastructure.

Backflow is more likely to occur if:

  • there's a drop in pressure in the main, eg during a main break, or due to high flow, e.g. during firefighting operations
  • water pressure at the property is higher than at the main, eg if a pump is operating on the site.

Backflow prevention devices ensure our water supply isn't contaminated from hazards from within a customer's property. These devices prevent potentially contaminated water in a customer's water service pipe flowing back into Council water main.


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