Melbourne
19.2 Leakage to landscape

The volume presented in the water accounting statements (10,779 ML) represents the volume of leakage resulting from pipe bursts and other losses to landscape from Melbourne's urban water distribution infrastructure and wastewater overflow to stormwater.

Leakage to landscape

Authority	Leakage type	Volume (ML)
City West Water	Non-revenue potable water –  pipe bursts	6,217
Melbourne Water	Losses from potable water supply system	992
South East Water	Non-revenue potable water –  pipe bursts	1,073
Western Water	Non-revenue potable water –  pipe bursts	862
Yarra Valley Water	Non-revenue potable water –  pipe bursts	1,635
Total		10,779

City West Water: database.

City West Water.

This item represents the real losses component of non-revenue water. Non-revenue water is calculated as bulk supplied water minus metered and billed domestic and non-domestic water consumption, and may be broken into four components;

• authorised unbilled
•  apparent losses (unauthorised)
•  apparent losses (metering)
• real losses (bursts, leaks and background losses).

This item is calculated from other figures, and its accuracy can be inferred from the other fields used to calculate the figures. 

+/– 5%

Melbourne Water: Waterworks database.

Melbourne Water.

Leakage to landscape (992 ML) represents the loss of potable water from major pipes, service reservoirs, tank water and other losses due to operational activities. Total loss volume is the sum of leakage and bursts.

The total loss volume is derived by the components in the following table.

Losses from potable water supply system

Losses from potable water supply system	Volume (ML)
Loss of potable water from major pipes	183
Loss of potable water through service reservoir and tanks water	28
Loss of potable water through operational activities	781
Total	992

A major loss event is when a water main requires isolation for repair works. This is generally when the leakage loss rate is greater than 1 ML/d.

Melbourne Water conducts separate investigations into all losses from major pipes. For each of these investigations, the total elapsed time, size of perforation and pressure of the leak is estimated to allow water loss to be calculated.

Dewatering is undertaken intermittently on service reservoirs and tanks to allow for cleaning and other maintenance works.

Service reservoirs and tanks have height meters that can accurately gauge current storage levels and water lost through dewatering.

This is a back calculation based on the volume supplied to retail water authorities and the volume received (billed) by retail water authorities.

Loss of potable water from major pipes is assumed to represent leakage to landscape.

Leakage from the non-potable water supplies is not included.

Non-potable water lost from aqueducts is not included as these are located upstream of the seasonal storages.

South East Water: various internal sources and database.

South East Water.

This item represents the estimated pipe bursts component of non-revenue water. The volume is estimated using a spreadsheet calculator based on multiple inputs in line with Infrastructure Leakage Index (ILI) standards.

The International Water Association has developed the ILI indicator to better represent the performance of water supply systems and their management in terms of leakage. The ILI is defined as the ratio of current annual real losses (CARL) to unavoidable annual real losses (UARL). CARL are determined from a conventional water balance undertaken on an annual basis. The UARL is a formula that accounts for the number of connections, the length of water mains and the average system operating pressure.

Nil.

The Water Industry Regulatory Audits Report 2011,  October 2011 (WIRA 2011) indicated that reliability and accuracy for the calculation of losses is +/–10% (i.e. Grade 3).

Western Water: Information Technology database.

Western Water.

Leakage from pipe bursts

Estimated losses from pipe bursts in the entire area that is supplied by Western Water, including the area outside the Melbourne region (i.e. Woodend). Losses are estimated by totaling all bulk meters, deducting metered totals downstream and deducting estimated background leakage.

Wastewater overflow to stormwater

The value is estimated by calculating the flow rate from SCADA and multiplied against the length of time of overflow.

Leakage from pipe bursts:

Volume represents losses applicable to the entire area supplied by Western Water. As such, it is an overestimate of the volume of losses applicable to the area within the region.

Wastewater overflow to stormwater:

Estimation only

+/— 5% in accordance with manufacturer's annual bulk meter test.

Yarra Valley Water 2010-2011 potable water balance.

Yarra Valley Water.

Yarra Valley Water use a reporting tool to log all pipe bursts and leaks reported in their service area. Each incident is categorised according to the size of the pipe and the severity of the incident.

In 2010–11, total loss through major pipe bursts was estimated to be 183 ML.

Nil.

Uncertainty is +/– 20% according to the Yarra Valley Water 2010–11 Reporting: Bulk Water, Non-Revenue Water and Residential & Commercial Potable Water Usage report for the Essential Services Commission.

The comparative year volume is unquantified.