Melbourne
10.6 Leakage from urban water system

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 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

^1–2 Combined pipe bursts and background leakage volume.

Internal database.

City West Water.

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

The uncertainty estimate is +/– 5%.

Waterworks database.

Melbourne Water.

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.

• 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.

The uncertainty estimate was not quantified.

Various internal sources and databases.

South East Water.

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

As appropriate to the standard method.

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

Information Technology database.

Western Water.

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.

• 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.

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

2012–13 potable water balance.

Yarra Valley Water.

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.

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

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.