Melbourne
19.20 Other urban water system decreases

The volume presented in the water accounting statements (11,301 ML) represents the sum of the following two components:

• the volume (11,249 ML) of non-revenue water from potable water supplies not including losses reported at line item 19.2 'Leakage to landscape' and 19.3 'Leakage to groundwater'
• the volume (52 ML) of non-potable water losses from treatment processes at Romsey and Lancefield water treatment plants.
  

The volume does not include leakage to groundwater or losses to the landscape, including pipe bursts from potable water supplies.

Non-revenue urban water system losses

Loss type	Water authority	2012 Volume (ML)
Non-revenue potable water other than pipe bursts and leakage	City West Water	2,325
	Melbourne Water	2,352
	South East Water	3,329
	Yarra Valley Water	3,243
Non-potable water losses	Western Water	52
Total		11,301

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.

Internal database.

City West Water.

Non-revenue water is calculated as bulk water supplied to users less metered and billed domestic and non-domestic water consumption. Non-revenue water may be broken into four components, authorised unbilled, apparent losses (unauthorised), apparent losses (metering) and reals losses (bursts, leaks and background losses).

The volume presented was calculated by subtracting real losses from the total non-revenue water.

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

Uncertainty is estimated to be +/– 5%.

Waterworks database.

Melbourne Water.

The volume of non-revenue potable water for Melbourne Water is the sum of the following two components:

• Loss of potable water through service reservoir and tank dewatering (580 ML)
• Loss of potable water through operational activities (1772 ML).

Potable water lost through service reservoir and tank dewatering

Dewatering is undertaken intermittently on service reservoirs and tanks to allow for cleaning and other maintenance works. Service reservoirs and tanks have height meters that can accurately gauge current storage levels and water lost through dewatering.

Loss of potable water through operational activites

The water required for operational activities and the lost through system shutdowns and flushing operations, and the volume of water required to carry out such operational activities is calculated. 

• Non-potable water supply losses are 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.

Internal database.

South East Water.

The volume presented was calculated by subtracting leakage and pipe-bursts from the total volume of non-revenue water (bulk water supplied minus water sales).

Non-revenue water includes infrastructure leakage, pipe burst, thefts and leak allowances.

Water Industry Regulatory Audits Report, October 2012 indicated that reliability and accuracy for metered volume of potable water delivered is +/– 5% (i.e. Grade 2).

Information Technology database.

Western Water.

The volume of water lost through treatment plant processes is estimated by taking the total surface water supply to the treatment plant and subtracting the total water supplied to the town.

Non-revenue water lost through treatment plant processes at Western Water's other treatment plants (not Romsey and Lancefield) was not included.

In accordance with the manufacturer's bulk test.

2011 and 2012 potable water balance.

Yarra Valley Water.

The volume of non-revenue potable water remaining was estimated by subtracting the volume of non-revenue water due to real losses (pipe bursts and leakage) from the total non-revenue water volume during the 2011–12 year.

Nil.

The uncertainty is estimated to be +/– 10%.

In the 2011 Account, non-revenue water volumes for Melbourne Water and Western Water were not reported.  In the 2012 Account, due to an improved understanding of the Melbourne region urban water system, these volumes are included at this line item.

Consequently, the volume has been restated from 9,138 ML (as published in the 2011 Account) to 10,127 ML as shown in the following table.

Comparative year information for line item 19.20 Other urban water system decreases

Loss type	Water authority	2012 Account volume at 30 June 2011 (ML)	2011 Account volume at 30 June 2011 (ML)
Non-revenue potable water other than pipe bursts and leakage	City West Water	2,238	2,238
	Melbourne Water	809
	South East Water	3,657	3,657
	Yarra Valley Water	3,423	3,423
Non-potable water losses	Western Water	n/a
Total		10,127	9,318

Notably, the volume of non-revenue water for Western Water was unavailable for the comparative year.