Melbourne
19.3 Leakage to groundwater

The volume presented (18,636 ML) represents leakage from Melbourne's urban water distribution system infrastructure to groundwater. The volume includes non-revenue potable, non-potable and recycled water leakage.

The breakdown of leakage to groundwater for retail water authorities in the Melbourne region during the 2010–11 year is presented in the following table.

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 supplies 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.

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.

+/– 10% in accordance with the WIRA 2011 independent annual audit report

This item represents the leakage subcomponent of non-revenue water. Background leakage and losses included 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 estimated background leakage is the leakage that occurs through Yarra Valley Water Infrastructure but cannot be identified.

Last year, Yarra Valley Water calculated this using their zone meters, which changed the methodology. This year, the bottom-up approach is unable to be implemented due to dynamic changes around the system, zone boundary changes and large billing meter errors (see billed metered consumption).

Calculation: This year the Background Leakage was used 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.

+/– 20%. This value also reflects the uncertainty in subcomponents used to calculate leakage as a residual from total non-revenue water.

This line item corresponds to both the following line items 20.2.2 Leakage from water distribution system to groundwater and15.2.4 Leakage from water distribution system to groundwater reported in the 2010 Account. There was no change to the volume reported in the 2010 Account. The comparative year volume is 19,403 ML.