19.8 Other wastewater discharge

Supporting information

a. Other wastewater discharge

The volume presented (8 ML) represents the volume of treated wastewater discharged to the landscape at the Whittlesea Sewage Treatment Plant (STP) when the recycled water storage dam is full.

b. Wastewater system overview

The wastewater system is one of three sub-components of Melbourne's urban water system. The three sub-components are the:

  • Urban water supply system
  • Wastewater system
  • Recycled water system.

In the Melbourne region, wastewater is collected (11.4) from users by the four retail water authorities within the region:

  • City West Water
  • South East Water
  • Western Water
  • Yarra Valley Water.

Following collection, wastewater is either delivered to smaller, local wastewater treatment plants operated by the authorities, or, more commonly, delivered to one of Melbourne Water's major wastewater treatment plants: the Eastern Treatment Plant and Western Treatment Plant. During the 2011–12 year Melbourne Water received and treated almost 90% of the wastewater collected within the region. The breakdown of the volumes of wastewater received by Melbourne Water's treatment plants and the authority's smaller treatment plants is presented in the following table.

Wastewater inflow for treatment received by Melbourne Water and the retail water authority's treatment plants

Water authority treatment plants

Volume (ML)

Melbourne Water

Western Treatment Plant


Eastern Treatment Plant1


City West Water


South East Water


Western Water


Yarra Valley Water




1 Includes 1,623 ML of treated wastewater received from Pakenham Sewage Treatment Plant.

During the 2011–12 year the majority (85%: 19.7) of treated wastewater was discharged to sea; approximately 11% was recycled and the remaining portion was discharged to surface water (3%: 19.5 ) and the landscape (<1%: 19.8).

The following figure shows all the inflows and outflows associated with the wastewater system. A small misbalance (> 1%) is shown. The misbalance can be attributed to metering inaccuracies, unaccounted losses and inaccuracies in the estimation of the recycled water on-site in process use.

For more detail on a particular flow associated with the wastewater system, refer to the line item notes. Note that volumes annotated with a * indicate flows between sub-components and are not reported in the account. As such, these flows do not have an associated line item number.

Schematic diagram of water inflows and outflows for Melbourne's wastewater system during the 2011–12 year. Line item numbers are provided in brackets.
Schematic diagram of water inflows and outflows for Melbourne's wastewater system during the 2011–12 year. Line item numbers are provided in brackets.

Quantification approach

Data source

Local treatment plants flow database (LPTFLOW).

Provided by

Yarra Valley Water.


Yarra Valley Water meters the volume of wastewater discharged from the treatment plant on a monthly basis.

Assumptions, limitations, caveats and approximations


Uncertainty information

The uncertainty is estimated to be +/– 5% based on meter specifications.