Melbourne
19.2 Leakage to landscape

The volume presented in the water accounting statements (3,354 ML) represents the volume of leakage resulting from pipe bursts from Melbourne's urban water supply system.

Leakage to landscape

Authority	Leakage type	Volume (ML)
City West Water1	Non-revenue potable water—pipe bursts	n/a
Melbourne Water	Losses—pipe bursts	129
South East Water	Non-revenue potable water—pipe bursts	1,052
Western Water2	Non-revenue potable water—pipe bursts	n/a
Yarra Valley Water	Non-revenue potable water—pipe bursts	2,173
Total		3,354

^1–2 A combined pipe bursts and background leakage volume was provided for these water authorities; the combined volumes are presented at line item 19.3 Leakage to groundwater.

The urban water supply 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.

During the 2011–12 year Melbourne's urban water was sourced exclusively from surface water [11.12]; however in some years a very small proportion is sourced from groundwater [11.13]. While a desalination plant has been built to supplement Melbourne's urban water supply, this was not operational during the 2011–12 year.

Urban water consumption [19.4] of potable and non-potable water was 330,632 ML during the 2011–12 year, representing almost 90% of all urban water supply system outflows. A very small volume of water was transferred out of the region via normal operations in Western Water's service area [19.11]. Non-revenue water, including pipes bursting [19.2], background leakage [19.3] and other losses [19.20], made up the remaining urban water supply system outflows.

The following figure shows all the inflows and outflows for the urban water supply system. For more detail on a particular flow associated with the urban water supply system, refer to the line item notes.

Schematic diagram of water inflows and outflows for Melbourne's urban water supply system during the 2011–12 year. Line item numbers are provided in brackets.

A small misbalance (0.1%) is shown in the previous figure and can be attributed to possible differences in metering accuracies and unaccounted losses associated with water intake and supply.

Waterworks database.

Melbourne Water.

Leakage to landscape is estimated to be the total loss through major pipe bursts.

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.

• 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.

The uncertainty estimate was not quantified.

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.

As appropriate to the standard method.

The Water Industry Regulatory Audits Report 2012, October 2012 report indicated that reliability and accuracy for the calculation of losses is +/–10% (i.e. Grade 3).

2011–2012 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.

Nil.

Uncertainty is +/– 20% according to the Yarra Valley Water 2011–12 water balance documentation report for the Essential Services Commission: Water balance Audit Document 2011–12.

In the 2011 Account, where pipe bursts and background leakage volumes were not quantified separately, the volume was reported at line item '19.2 leakage to landscape'.

In the 2012 Account, where the pipe bursts and background leakage volumes were not quantified separately, this volume was reported at line item 19.3 Leakage to groundwater in order to be consistent with the classification of urban water leakage applied to the other regions of the National Water Account.

Consequently, the volume has been restated from 10,779 ML (as published in the 2011 Account) to 2,892 ML.

Restatement of comparative year information for line item 19.2 Leakage to landscape

Authority	2012 Account volume for the 2010–11 year (ML)	2011 Account volume for the 2010–11 year (ML)
City West Water	0	6,217
Melbourne Water	183	992
South East Water	1,074	1,073
Western Water	0	862
Yarra Valley Water	1,635	1,635
Total	2,892	10,779