19.2 Urban water system leakage to landscape

Supporting information

a. Leakage to landscape

The volume presented in the water accounting statements (4,398 ML) represents the volume of leakage resulting from pipe bursts from Melbourne's urban water supply system.

Leakage to landscape from urban water system
Authority Leakage type Volume (ML)
City West Water1 non-revenue potable water—pipe bursts  n/a
Melbourne Water losses—pipe bursts
South East Water non-revenue potable water—pipe bursts  1,089
Western Water2 non-revenue potable water—pipe bursts n/a
Yarra Valley Water non-revenue potable water—pipe bursts 3,271
Total 4,398

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.

b. Urban water supply system overview

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 2012–13 year Melbourne's urban water was sourced mostly from surface water (line item 11.12), with a very small proportion sourced from groundwater (line item 11.13). While a desalination plant has been built at Wonthaggi to supplement Melbourne's urban water supply, this was not required to supply any water during the 2012–13 year.

Urban water consumption (line item 19.4) of potable and non-potable water was 361,339 ML during the 2012–13 year, comprising of 360,931 ML of potable water and 408 ML of non-potable water, 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 (line item 19.11). Non-revenue water, including pipes bursting (line item 19.2), background leakage (line item 19.3) and other losses (line item 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 2012–13 year; line item numbers are provided in brackets
Schematic diagram of water inflows and outflows for Melbourne's urban water supply system during the 2012–13 year; line item numbers are provided in brackets

A small misbalance 127 ML from the previous figure can be attributed to possible differences in metering accuracies and unaccounted losses associated with water intake and supply.

Quantification approach

Melbourne Water

Data source

Waterworks database.

Provided by

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.

Assumptions, limitations, caveats and approximations

  • 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.

Uncertainty information

The uncertainty estimate was not quantified.

South East Water

Data source

Various internal sources and databases.

Provided by

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.

Assumptions, limitations, caveats and approximations

As appropriate to the standard method.

Uncertainty information

The Water Industry Regulatory Audits Report 2013, report indicated that reliability and accuracy for the calculation of losses is +/–10% (i.e. Grade 3).

Yarra Valley Water

Data source

2012–2013 potable water balance.

Provided by

Yarra Valley Water.


Yarra Valley Water uses 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.

Assumptions, limitations, caveats and approximations


Uncertainty information

Uncertainty is +/– 20% according to the Yarra Valley Water 2012–13 water balance documentation report for the Essential Services Commission: Water balance Audit Document 2012–13.