Water treatment

To make sure Melbourne has safe drinking water, we treat and disinfect it before it leaves our reservoirs and enters the water supply system.

The processes we use depend on the source of water: most comes from protected catchments and only needs to be disinfected, whereas water from open catchments is fully treated at our treatment plants.

Water treatment processes

The full treatment process has additional steps to filter out impurities before water is disinfected.


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

Clarification or floatation

Particles are made to sink or float to separate them from the water, allowing them to be easily removed. Depending on the treatment plant, this stage uses:

  • mechanical settling basins, called clarifiers
  • diffusers, which create fine bubbles that stick to particles to make them float​


Filters or membranes remove most of the remaining particles as water passes through them. Types of filters include:

  • gravity media filters with layers of sand
  • membrane filters with billions of microscopic pores​


Chlorine, chloramine (chlorine and ammonia) or ultraviolet light destroy any disease-causing bacteria. The amount of chlorine added varies, but is typically less than one milligram per litre (0.0001%), or one grain of sugar in a cup of water.


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

pH correction

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

Water treatment plants

We operate two large treatment plants, Winneke and Tarago, which treat water from open catchments. Several smaller plants treat water from protected catchments, including:

  • three smaller membrane filtration plants supplying Healesville and Yarra Glen
  • six UV disinfection plants
  • chlorination plants located at all major water treatment plants

Winneke Water Treatment Plant

Built at Sugarloaf Reservoir in 1980, Winneke was the first treatment plant to supply Melbourne with fully treated water. It uses sand filtration to provide about one-quarter of Greater Melbourne’s drinking water.

Tarago Water Treatment Plant

The Tarago plant was completed in 2009 to reconnect Tarago Reservoir to Melbourne’s water supply network, increasing our drinking water supplies during the Millennium Drought. It uses a dissolved air flotation and filtration process.

Last updated:
11 December 2019