Melbourne

The volume recognised in the water accounting statements (8,760 ML) represents leakage from urban water distribution system infrastructure for each of the water utilities operating in the Melbourne region.

The total volume does not include losses from the wastewater collection network or recycled water supply networks.

Where the fraction of leakage entering groundwater was not available, the volume of total losses including leakage was reported here as an input to the landscape.

The table below shows the breakdown of leakage for each water utility within the Melbourne region during 2009–10.

Data sources

Melbourne Water: Waterworks database.
Yarra Valley Water: bursts and leakage database.
South East Water: various internal sources.
City West Water: unaccounted-for water spreadsheet.
Western Water: IT database.

Data provider

Melbourne Water, Yarra Valley Water, South East Water, City West Water and Western Water.

Method

The total volume of leakage from the water distribution system to the landscape is the sum of a number of components that are provided from different water utilities. The method for each provider is described below.

Melbourne Water
This item represents the estimated losses and leakage from the water supply systems managed by Melbourne Water. These systems range from intake of water from seasonal storages for treatment, to the delivery of potable water to other water utilities. The total volume was derived by the addition of the following components:

• Potable water lost from pipes (major pipes)
  A major loss event is defined as when a water main requires isolation for repair works. This is generally when the leakage loss rate is greater than 1 ML/d.
  Melbourne Water conducts separate investigations into all losses from major pipes. For each of these investigations, the total elapsed time, size of perforation and pressure of the leak is estimated to allow leakage loss to be calculated.
  In 2009–10, the total loss through major pipe bursts was estimated to be 33 ML.
  
  
• Potable water lost from pipes (minor leaks)
  A minor loss event is defined as when a water main does not require isolation for repair works. This is generally when the leakage loss rate is less than 1 ML/d.
  For losses from minor pipes, Melbourne Water has adapted an estimation method determined by the Australian Water Association (AWA).
  Melbourne Water keeps records of the time taken to repair each leak in its system and, in 2009–10, the total loss through minor pipe bursts was estimated to be 79 ML.
  
  
• Potable water lost through service reservoir and tank dewatering
  Dewatering is undertaken on service reservoirs and tanks intermittently 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.
  In 2009–10, the total loss due to dewatering of service reservoirs and tanks was estimated to be 249 ML.
  
  
• Potable water lost through operational activities
  Water can be lost through system shutdowns and flushing operations.
  The volume of water required to carry out such operational activities is calculated.
  In 2009–10, the total loss through operational activities was estimated to be 862 ML.
  Note that non-potable losses from the Melbourne Water system upstream of seasonal storages are not considered to be part of the water distribution system and are consequently not reported.
  

Western Water
This item represents the estimated losses from pipe bursts in the entire area supplied by Western Water, including the area outside of the Melbourne region subaccount (around Woodend). Losses were estimated by totalling all bulk meters, deducting metered totals downstream and deducting estimated background leakage.

City West Water
This item represents the total losses and leakage from the potable water supply system. It is part of the nonrevenue water component that is attributed to losses and leakage.

City West Water maintains a database of bursts and leaks that occur in their service area throughout the year. The volume of water lost from bursts and leakage was estimated by multiplying the time taken (in minutes) to fix the burst or leak by an average flow rate for the pipes where the leak occurred.

Yarra Valley Water
This item represents the losses from pipe bursts from Yarra Valley Water infrastructure, which was a component of nonrevenue water.

Yarra Valley Water maintains a database of bursts and leaks that occur in their service area throughout the year. The volume of water lost from bursts and leakage was estimated by multiplying the time taken (in minutes) to fix the burst or leak by an average flow rate for the pipes where the leak occurred.

South East Water
This item represents the estimated pipe bursts component of nonrevenue water. The volume was estimated using a spreadsheet calculator based on multiple inputs in line with Infrastructure Leakage Index (ILI) standards.

The International Water Association has developed the ILI standards to better represent the performance of water supply systems and their management of leakage. The ILI is defined as the ratio of Current Annual Real Losses (CARL) to Unavoidable Annual Real Losses (UARL). CARL was determined from a conventional water balance undertaken on an annual basis. The UARL is a formula that accounts for the number of connections, the length of water mains and the average system operating pressure.

Uncertainty

Melbourne Water: Ungraded.
Western Water: Ungraded.
City West Water: Estimated uncertainty is +/–5%.
Yarra Valley Water: Estimated uncertainty is +/–20%.
South East Water: Estimated uncertainty is +/–10%.

Uncertainty values provided by City West Water, Yarra Valley Water and South East Water refer to the Essential Services Commission’s standard confidence grades, as detailed in its June 2005 guideline for Approving, Conducting and Reporting Audits for Victorian Water Businesses (ESC 2005). Refer to Summary Audit Report – Regulatory Audit of AGL Energy Limited, October 2010 (ESC 2010) prepared individually for City West Water, Yarra Valley Water and South East Water.

Approximations, assumptions, caveats/limitations

Melbourne Water
Loss and leakage from the non-potable water supplies was not included.
Non-potable water lost from aqueducts was not included as the aqueducts are located upstream of the seasonal storages.

Western Water
The volume of losses provided by Western Water represents the entire service area of Western Water, including a small area outside of the Melbourne region subaccount (around Woodend). As such, the figure provided was an overestimate of the volume of losses applicable to the area within the region.

City West Water
Average flow rates used for the calculation of bursts or leaks were based on limited historical flow rate data from bursts and leaks, including analysis of SCADA data, Melbourne Water’s methodology based on the size of the leak, and the pressure and bucket tests in the field to measure the rate of leak.

Yarra Valley Water
Average flow rates used for the calculation of bursts or leaks were based on limited historical flow rate data from bursts and leaks, including analysis of SCADA data, Melbourne Water’s methodology based on the size of the leak, and the pressure and bucket tests in the field to measure the rate of leak.

South East Water
Other than the total volume of nonrevenue water volumes, all other nonrevenue water volumes were calculated based on assumptions. Refer to Summary Audit Report – Regulatory Audit of AGL Energy Limited, October 2010 (ESC 2010) prepared for South East Water.