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The volume recognised in the water accounting statements (19,403 ML) represents leakage from urban water distribution system infrastructure for each of the water utilities operating in the Melbourne region.

The total volume does not include leakage from the wastewater collection network or recycled water supply networks.

Where the fraction of leakage entering groundwater was not available, the volume of total losses including leakage was reported as an input to the landscape under Line item 20.2.1.

The following table shows the breakdown of leakage for each water utility within the Melbourne region during 2009–10.

Volume of leakage to groundwater for each water utility within the Melbourne region

Infrastructure operator	Volume (ML)
City West Water	0
Melbourne Water	0
South East Water	7,885
Western Water	964
Yarra Valley Water	10,554
Total	19,403

Data source

Western Water: IT database.
Yarra Valley Water: quarterly billing database; billing verification database.
South East Water: various internal sources.

Data provider

Western Water, Yarra Valley Water and South East Water.

Method

The total volume of leakage from the water distribution system to groundwater was the sum of a number of components that are provided from different water utilities. City West Water did not provide this information. Melbourne Water included this leakage with that going to landscape.

Western Water
This item represents estimated leakage from the entire area supplied by Western Water, including the area outside of the Melbourne region subaccount (around Woodend). Background leakage was calculated by deducting volumes from bulk meter totals, and deducting all metered usage and estimated losses downstream of bulk meters.

Yarra Valley Water
This item represents leakage from Yarra Valley Water infrastructure, which was a component of nonrevenue water. Background leakage was calculated by subtracting the sum of all nonrevenue water components from the metered volume of water received from the bulk supplier.

South East Water
This item represents the estimated leakage component of nonrevenue water. The leakage component was estimated using the Water Services Association of Australia (WSAA) Benchloss software model.

Uncertainty

Western Water: Estimated uncertainty is ungraded.
Yarra Valley Water: Estimated uncertainty is +/–20%.
South East Water: Estimated uncertainty is +/–10%.

Uncertainty values provided by Yarra Valley Water and South East Water refer to the Essential Services Commission’s standard confidence grades, as detailed in its June 2005 guideline for Approving, Conducting and Reporting Audits for Victorian Water Businesses (ESC 2005). Refer to Summary Audit Report – Regulatory Audit of AGL Energy Limited, October 2010 (ESC 2010) prepared individually for Yarra Valley Water and South East Water.

Approximations, assumptions, caveats/limitations

Western Water
The volume of losses provided by Western Water represents the entire service area of Western Water, including a small area outside of the Melbourne region subaccount (around Woodend). As such, the figure provided was an overestimate of the volume of losses applicable to the area within the region.

Yarra Valley Water
Nonrevenue water consists of numerous components, each estimated using a wide range of approaches and assumptions. For more information, refer to Summary Audit Report – Regulatory Audit of AGL Energy Limited, October 2010 (ESC 2010) prepared for Yarra Valley Water.

South East Water
Nonrevenue water consists of numerous components, each estimated using a wide range of approaches and assumptions. For more information, refer to the Summary Audit Report – Regulatory Audit of AGL Energy Limited, October 2010 (ESC 2010) prepared for South East Water.