Water treatment

Treating water protects our health by making sure safe drinking water is supplied to Melbourne.

Most of our drinking water needs very little treatment, as it comes from protected catchments which supply high quality water. This water is disinfected as it leaves our storage reservoirs and enters the supply system.  

Some of our water comes from unprotected catchments and is fully treated at our water treatment plants. This process has additional steps to remove impurities before the water is disinfected, and is similar to water treatment processes used throughout the world.

Water treatment processes

Step 1


Chemicals – usually liquid aluminium sulphate (alum) – are added to help bacteria and small solid particles stick together, forming larger particles.

Step 2

Clarification (and floatation)

Mechanical settling basins called clarifiers use gravity to separate out solid particles and remove colour.

Water at Tarago treatment plant undergoes a floatation process, where a diffuser creates fine bubbles that stick to the particles. This causes them to float to the surface of the water where they can be removed.​

Step 3


Most of the remaining particles are removed as water passes through filters or membranes, with the method varying between treatment plants:

  • gravity media filtration uses filters containing layers of sand or coal
  • membrane filtration uses semi-permeable membranes with billions of microscopic pores​ 

Step 4


Chlorine, chloramine (chlorine and ammonia) or ultraviolet light are used to destroy any disease-causing bacteria.

The amount of chlorine added varies, but is typically less than one milligram per litre (0.0001%), or one sugar grain in a cup of water.  

Step ​5


Fluoride is added in small amounts – less than one milligram per litre – to help prevent tooth decay. This is a legal requirement under the Health (Fluoridation) Act 1973, administered by the Department of Health.

Further information is on the Department of Health website.

Step 6

pH correction

Lime, caustic soda or soda ash is added to neutralise the pH of the water as chlorine and fluoride are slightly acidic. The minerals in lime also help prevent household pipes and fittings from corroding. 

Water treatment plants

We operate two large filtration plants which treat water from unprotected catchments:

  • Winneke Water Treatment Plant at Sugarloaf Reservoir
  • Tarago Water Treatment Plant at Tarago Reservoir

We also have several other plants which treat water from protected catchments, using disinfection, fluoridation and pH correction processes.

​Summary of treatment processes at each plant

Plant Coagulation Clarification Filtration​ Disinfection​ Fluoridation ​pH correction
Plants supplying Melbourne​ ​ ​ ​ ​ ​ ​
Cardinia​ Chlorine​ •​ •​
​Greenvale Chlorine​
Silvan​ Chlorine​ •​ •​
Tarago​ •​ Floatation​ Gravity​ Chlorine​ •​ •​
Winneke​ •​ •​ Gravity​ Chlorine​ •​ •​
Yan Yean​ •​ Gravity​ Chlorine​ •​ •​
​​Plants supplying local townships
Healesville Membrane Chlorine​ •​
Kallista​ Chloramination •​
Monbulk​ Chloramination •​
Warburton UV + chlorine​
East Warburton UV + chlorine​
Woori Yallock UV + chlorine​
Yarra Glen​ Membrane Chlorine​ •​
Yarra Junction​ UV + chlorine​

Detailed information on each plant's treatment process is available in our Water Quality Annual Report:

Did you know?

In 1980 Winneke Water Treatment Plant first introduced fully treated water to Melbourne, marking a milestone in the history of our water supply system.

History of our water supply system

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