Melbourne
10.6 Leakage from urban water system

The volume presented (28,352 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 2011–12 year is presented in the following table. 

Leakage from urban water system

Water authority	Volume (ML)
City West Water1	6,622
Melbourne Water	20
South East Water	12,380
Western Water2	921
Yarra Valley Water	8,409
Total	28,352

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

Internal 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. 

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 2012 independent annual audit report.

Information Technology database.

Western Water.

This item represents the estimated losses from pipe bursts, leakage 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). Water losses are estimated as 8.46% of the total amount of water produced/provided by Western Water.

• Assumes that 8.46% of total water supplied is attributed to non revenue losses.
• The percentage of 8.46% is an evolving figure based on bulk water supplied minus metered and billed water consumption for given time periods.
  
• As pipe bursts, background leakage and other non-revenue cannot be separated they are reported collectively as leakage from the urban water system to groundwater.

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

2011–12 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 of non-revenue water.

Non-revenue water consists of the following subcomponents:

• hydrant usage
• trunk services (leakage)
• Yarra Valley Water's own use (flushing and cleaning)
• fire authorities (firefighting 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).

Sub-component volumes are estimated using a wide range of approaches.

The volume of background leakage was estimated as the balancing item for the water balance.

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.

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 10.6 'Leakage from urban water system' 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 18,636 ML (as published in the 2011 Account) to 25,715 ML.

Comparative year information for line item 10.6 Leakage from urban water system

Authority	2012 Account volume for the 2010–11 year (ML)	2011 Account volume for the 2010–11 year (ML)
City West Water	6,217	0
Melbourne Water	75	75
South East Water	9,907	9,907
Western Water	862	0
Yarra Valley Water	8,654	8,654
Total	25,715	18,636