Melbourne
19.6 Discharge from urban water system to irrigation scheme

Supporting information

a. Discharge from urban water system to irrigation scheme

The volume presented in the water accounting statements (8,076 ML) represents the metered volume of recycled water provided by the Melbourne Water Eastern Treatment Plant to the Eastern Irrigation Scheme, and the Melbourne Water Western Treatment Plant to the Werribee Irrigation District.

Recycled water supplied to irrigation schemes
Wastewater treatment plant  Irrigation scheme

Volume (ML)

Melbourne Water Western Treatment Plant Werribee Irrigation District

2,309

Melbourne Water Eastern Treatment Plant Eastern Irrigation Scheme

5,767

Total

8,076

b. Recycled water system overview

The recycled water system is one of three subcomponents of Melbourne's urban water system. The three subcomponents are the:

  • urban water supply system
  • wastewater system
  • recycled water system.

In the Melbourne region, wastewater treatment plants located within the region operated by water authorities produce the majority of recycled water (see 'Wastewater system overview' for further information). A very small volume of recycled water (161 ML; line item 11.21) is received from external organisations (also located within the region) to supplement Melbourne's recycled water system.

During the 2012–13 year, approximately 45% of the recycled water produced (including the recycled water received from external organisations) was used on-site at wastewater treatment plants throughout the Melbourne region.  Of the recycled water used on-site, approximately half that volume (15,118 ML) was recirculated back into the wastewater system (and therefore not reported in the water accounting statements). The remaining recycled water used on-site was for irrigation/outdoor purposes or in-process and reported at line item 19.4.

The remaining recycled water produced in Melbourne was supplied for use; 8,511 ML was supplied to urban water system users (line item 19.4); and 8,076 ML was supplied to either the Eastern Irrigation Scheme and Werribee Irrigation district (line item 19.6). Recycled water was also supplied for environmental purposes to Lake Borrie Wetlands within the Western Treatment Plant (line item 19.5).

The following figure presents the inflows and outflows associated with the recycled water system. A small misbalance (1.6%) is shown, due to the difference between the volume of recycled water available for supply and the volume of recycled water supplied for use. 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 recycled water system, refer to the line item notes. Note that volumes annotated with an asterisk (*) indicate flows between urban subcomponents and are not reported in the 2013 Account.  As such, these flows do not have an associated line item number or note.

Schematic diagram of water inflows and outflows for Melbourne's recycled system during the 2012–13 year; line item numbers are provided in brackets
Schematic diagram of water inflows and outflows for Melbourne's recycled system during the 2012–13 year; line item numbers are provided in brackets

Quantification approach

Data source

Various utility databases.

Provided by

Melbourne Water.

Method

Recycled water supplied to the Eastern Irrigation Scheme (and other urban water authorities) is measured with magnetic flow meters at the interface of Melbourne Water and the receiving authority. The Melbourne Water Western Treatment Plant logs data daily and report quarterly, and Melbourne Water Eastern Treatment Plant logs data daily and reports monthly.

Assumptions, limitations, caveats and approximations

Nil.

Uncertainty information

Magnetic flow meters are used to measure these flows and are assumed to have an accuracy in the range of +/–1% to +/–2%.