Melbourne
11.21 Other urban water system increases

Supporting information

a. Other urban water system increases

The volume reported in the water accounting statements (161 ML) represents recycled water purchased by South East Water from TopAq Eastern Irrigation Scheme. This augments the recycled water received by South East Water from the Melbourne Water Eastern Treatment Plant and is subsequently supplied to users.

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

Internal database.

Provided by

South East Water.

Method

The volume reported was calculated by summing the quarterly metered volumes of recycled water purchased by South East Water from TopAq Eastern Irrigation Scheme.

Assumptions, limitations, caveats and approximations

  • Assumes meters and readings are accurate.
  • The TopAq Eastern Irrigation Scheme meter-reading cycle does not align with the 1 July 2012–30 June 2013 reporting period; however, it does cover a 12-month period that is consistently applied each year.

Uncertainty information

The uncertainty is estimated to be +/– 5% in accordance with the Water Industry Regulatory Audits 2013 independent annual audit report.