Melbourne
19.20 Other urban water system decreases

The volume presented in the water accounting statements (11,638 ML) represents the sum of the following components:

• the volume (11,105 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 (130 ML) of non-potable water losses from treatment processes at Romsey and Lancefield water treatment plants.
• the volume (403 ML) of other wastewater losses
  

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

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.

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. 

The volume of other wastewater losses was estimated by subtracting the total volume of treated wastewater outflows including evaporation from the total volume of wastewater inflow to the Altona treatment plant and Sunshine sewer mining plant during the 2012–13 year.

Uncertainty is estimated to be +/– 5%.

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 (163 ML)
• loss of potable water through operational activities (2,131 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 activities

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

• 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.

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 2013, independent annual report indicated that reliability and accuracy for metered volume of potable water delivered is +/– 5% (i.e. Grade 2).

This item represents the metered volume of treated wastewater discharged from Pakenham sewage treatment plant (STP) at Melbourne Water Eastern Treatment Plant in 2012-13.

Meters and readings are accurate. Based on further information provided by Melbourne Water on this volume of treated effluent transferred to Melbourne Water Eastern Treatment Plant.

+/–5% in accordance with the Water Industry Regulatory Audits 2013 independent annual audit report.

Western Water.

The volume of water lost through treatment plant processes is estimated by taking the total 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 treatment plants other than Romsey and Lancefield was not included.

The volume of non-revenue potable water remaining  represents the estimated losses from pipe bursts, leakage, unbilled water (Western Water use, Country Fire Authority use) and other loses (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).

Assume that's 12.67% of total water supplied is attributed to non-revenue loses. 

The uncertainty is estimated to be +/– 5% in accordance with Summary Audit Report – October 2011 (ESC 2011)

This item represents the subcomponents of non-revenue water except the components representing real losses (leakage and pipe bursts). The volume representing each subcomponent is estimated using a variety of estimation methodologies.