Melbourne
19.3 Urban water system leakage to groundwater

Supporting information

a. Leakage to groundwater

The volume presented (31,529 ML) represents leakage from Melbourne's urban water supply system to groundwater. Where a combined volume for losses due to pipe bursts and background leakage is provided, this volume is also reported here as leakage to groundwater.

The breakdown of leakage to groundwater for water authorities in the Melbourne region during the 2012–13 year is presented in the following table. 

Leakage to groundwater from urban water system
Water authority Volume (ML)
City West Water1
7,114
Melbourne Water
21
South East Water 10,917
Western Water2
1,569
Yarra Valley Water 11,908
Total 31,529

1 Combined pipe bursts and background leakage volume

2 Combined pipe bursts, background leakage and other non-revenue water volume

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

City West Water

Data source

Internal database.

Provided by

City West Water.

Method

This item represents the real losses component of the non-revenue water. It represents the combined volume of pipe bursts, leakages and background losses.

Assumptions, limitations, caveats and approximations

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

Uncertainty information

The uncertainty estimate is +/– 5%.

Melbourne Water

Data source

Waterworks database.

Provided by

Melbourne Water.

Method

Leakage to groundwater is estimated to be the total loss of potable water due to minor leaks.

A minor loss event is when a water main does not require isolation for repair works. This is generally when the leakage loss rate is less than 1 ML/day.

For losses from minor pipes, Melbourne Water has adapted an estimation method determined by the Australian Water Association. Melbourne Water keeps records of the time taken to repair each leak in its system.

Assumptions, limitations, caveats and approximations

  • Leakage from the non-potable water system 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.

Method

This item represents the estimated leakage component of non-revenue water (based on the Water Services Association of Australia Benchloss software).

Assumptions, limitations, caveats and approximations

As appropriate to the standard method.

Uncertainty information

The uncertainty estimate is +/– 10% in accordance with the Water Industry Regulatory Audits 2013 independent annual audit report.

Western Water

Data source

Information Technology database.

Provided by

Western Water.

Method

This item represents the estimated losses from pipe bursts, leakage, flow to waterways for large bursts, unbilled water (Western Water use, Country Fire Authority use) and other losses (theft, filling of pipe work in construction, and meter error) within the area supplied by Western Water within the Melbourne region (i.e., excluding Woodend supply area). Non-revenue water is estimated as 12.67% of the total amount of water produced/provided by Western Water.

Assumptions, limitations, caveats and approximations

  • Assumes that 12.67% of total water supplied is attributed to non-revenue losses.
  • The percentage of 12.67% is an evolving figure based on bulk water supplied minus metered and billed water consumption for given time periods.

Uncertainty information

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

Yarra Valley Water

Data source

2012–13 potable water balance.

Provided by

Yarra Valley Water.

Method

This item represents the leakage subcomponent of non-revenue water. Background leakage and losses are calculated as the total volume of non-revenue water minus the sum of all other subcomponents.

Non-revenue water consists of the following subcomponents:

  • hydrant usage
  • trunk services (leakage)
  • Yarra Valley Water's own use (flushing and cleaning)
  • fire authorities (fire fighting and testing)
  • fire services (testing)
  • fire services (unauthorised use)
  • illegal connections and meter tampering
  • unauthorised use of hydrants and permit underestimates
  • meter sizing (not registering)
  • under-registration
  • Yarra Valley Water mains leakage (i.e., bursts).

Subcomponent volumes are estimated using a wide range of approaches.

This year, the volume presented as background leakage includes the estimated volume of leakage from the unmetered trunk services.

Assumptions, limitations, caveats and approximations

Leakage is assumed to be the residual of total non-revenue water and the various estimated subcomponents.

Uncertainty information

The uncertainty estimate is +/– 20%. This value also reflects the uncertainty in subcomponents used to calculate leakage as a residual from total non-revenue water.