11.21 Other urban water system increases
a. Other urban water system increases
The volume reported in the water accounting statements (237 ML) represents recycled water purchased by South East Water. This augments the recycled water received by South East Water from the Eastern Treatment Plant and is subsequently supplied to users.
b. Recycled water system overview
The recycled water 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 treatment plants located within the region produce the majority of recycled water (see 'wastewater system overview' for further information). A very small volume of recycled water (237 ML : 11.21) is received from external organisations to supplement Melbourne's recycled water system.
During the 2011–12 year, approximately 70% 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 (14,876 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; 8,415 ML was supplied to urban water system users [19.4]; and the remaining volume (3,089 ML) was supplied to either the Eastern Irrigation Scheme or Werribee Irrigation District [19.6].
The following figure presents the inflows and outflows associated with the recycled water system. A small misbalance (1.1%) 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 a * indicate flows between urban sub-components and are not reported in the 2012 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 2011–12 year. Line item numbers are provided in brackets.
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 2011 – 30 June 2012 reporting year; however, it does cover a 12-month period that is consistently applied each year.
The uncertainty is estimated to be +/– 5% in accordance with the Water Industry Regulatory Audits 2012 independent annual audit report.
In the 2011 Account inflows to the urban water system received via purchased recycled water were not reported.
In the 2012 Account, due an improved understanding of the urban water system balance, this inflow to the urban water system was reported at line item 11.21 'Other urban water system increases'.Consequently, the volume has been restated as 140 ML as shown in the following table.
|Recycled water received from other organisations within the region||2012 Account volume for the 2010–11 year (ML)||2011 Account volume for the 2010–11 year (ML)|
|Recycled water purchased from TopAq Eastern Irrigation Scheme||139||not reported
|Recycled water received from Inkerman Greywater treatment plant||1||not reported