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Treatment process

To ensure a safe water supply, water is treated and/or disinfected before it is supplied to customers.

Greater Western Water’s water treatment processes are determined by a range of factors including:

  • the catchment area
  • the chemistry and biology of the water
  • mandatory requirements, such as disinfection and fluoridation.

Drinking water sourced from unprotected catchments (all local water storages) requires filtration and disinfection due to the surrounding agricultural and urban activity. Water sourced from Melbourne is from protected catchments so only requires disinfection.

How we treat water


Disinfection is important in order to destroy potentially harmful micro-organisms in the water supply to maintain public health. This process kills any bacteria or viruses in the water and provides a residual effect to protect the water from recontamination as it travels through the distribution system. Chlorine or chloramines are used to disinfect the water supply.


Chlorination is the addition of chlorine as a gas or a hypochlorite solution to the water supply to destroy micro-organisms. The water supply in smaller towns responds most effectively to chlorine because the pipe network is smaller.


Chloramination is the addition of ammonia to chlorine, which forms chloramines. Chloramines are less reactive than chlorine alone which enables them to travel further into the distribution system and safely maintain disinfection of the water supply. Chloramines are also less likely to generate taste and odour issues, compared to chlorine alone.

pH correction

Acidity is corrected to provide a neutral pH by adding small quantities of lime or soda ash to the water. This ensures the water does not corrode our water mains and also maintains disinfection throughout the system.

How water is treated in your system

In the area previously serviced by Western Water, Greater Western Water filters water to remove naturally occurring particles, and adds measured doses of chemicals to provide you with safe and healthy drinking water.

Different supply systems have different treatment requirements. The type of treatment provided to our various supply sources are described below. More information can be found in our Water Quality Report.

Water supply sourceTreatment process
Lake MerrimuSedimentation, pH correction, filtration, fluoridation and disinfection (chlorination)
Rosslynne ReservoirCoagulation, pH correction, dissolved air flotation, filtration, fluoridation and disinfection (chlorination)
Melbourne (Greenvale Reservoir, via Hillside Pump Station)Pre-fluoridation, pre-chlorination followed by additional secondary disinfection (chlorination)
Melbourne (Greenvale Reservoir, via Loemans Road Pump Station)Pre-Fluoridation, pre-chlorination followed by secondary disinfection (chlorination)
Campaspe Reservoir & Reservoir CCoagulation, pH correction, dissolved air flotation, filtration and disinfection (chlorination)
Kerrie ReservoirMicrofiltration, pH correction, and disinfection (chloramination)
Garden Hut ReservoirCoagulation, pH correction, dissolved air flotation, filtration, disinfection (chlorination)
Pykes Creek ReservoirCoagulation, pH correction, dissolved air flotation, filtration, and disinfection (chlorination)


In accordance with the requirements set by the Victorian Department of Health and Human Services, some water supplies have fluoride added for dental health benefits.

The table below highlights the towns within Greater Western Water’s region (in the area previously serviced by Western Water) which receive a fluoridated and non-fluoridated supply.

Fluoridated water suppliesNon-fluoridated water supplies
Diggers Rest
Mount Macedon
Riddells Creek
Bacchus Marsh
Melton South

*These towns only receive fluoridated water when supplied with water from outside their normal water source. For example, in times of drought water may come from Melbourne or be brought in from other sources. The long term levels of fluoride during these times are below what is expected from a normal fluoridated water supply.

For more information about fluoride, visit the Department of Health and Human Services website or call their hotline on 1300 761 874.