19.3 Leakage to groundwater

Supporting Information

This line item refers to leakage from the urban water system into groundwater aquifers. Total leakage from each urban water supply area is given in the following table.


Total leakage into groundwater aquifers from the urban water system during the 2010–11 year


Leakage (ML)

Perth city







Quantification Approach

Data Source

Water Corporation: Operational Data Storage System and Facilities Mapping System.

Provided by

Water Corporation.


Leakage from the urban water system (defined as real losses) was calculated using the following equation:


Real losses = non-revenue water – (apparent losses + unmetered authorised consumption)


Non-revenue water is water that is lost before it reaches the customer. The volume of non-revenue water is calculated by subtracting the metered volume of water consumed (revenue water) from the metered volume of water supplied. The revenue water was first adjusted to take into account the difference between total water delivered bulk meter readings (done daily) and the customer meter readings (done twice per year for each customer). This is known as the meter lag adjustment.

The volume of apparent losses comprises two components – unauthorised consumption (e.g. water theft) and customer meter under-registration (e.g. meter inaccuracies). The unauthorised consumption is assumed to be 0.1% of the metered volume of water supplied. Customer meter under-registration is assumed to be 2% of revenue water.

The volume of unmetered authorised consumption is calculated as 0.5% of the metered volume of water supplied.

Assumptions, Limitations, Caveats and Approximations

There is no differentiation between leakage to the landscape and leakage to the groundwater store, it is simply assumed, in this case, that all losses go to the groundwater store.

The volumes of apparent losses and unmetered authorised consumption are not measured and are estimated based on the Infrastructure Leakage Index for Perth and Mandurah.

Uncertainty Information

The uncertainty estimate was not quantified.

Comparative year

The following table presents substantive changes in the line item reported in this 2011 Account with the corresponding line item in the 2010 Account.


Comparative year information for line item 19.3

2011 Account line item

2010 Account line item

2011 Account volume for the 2009–10 year (ML)

2010 Account volume for the 2009–10 year (ML)

Change from the 2010 Account to the 2011 Account

19.3 Leakage to groundwater

20.2.2 Leakage from water distribution system to groundwater



Change in line item name and number