19.4 Delivery to urban water system users

Supporting Information

This line item refers to the total volume of water supplied from the urban water system to urban users within the Perth region.

Quantification Approach

Data Source

Water Corporation: Operational Data Storage System.

Provided by

Water Corporation.


Total water supply to urban users within the Perth region during the 2010–11 year is calculated as shown in the following table.


Total water supplied to urban users during the 2010–11 year



Volume (ML)


11.12 Surface water diversion



11.13 Groundwater extraction



11.6 Desalinated water



Total water abstracted



9.9 Internal transfers



Riparian releases(a)



10.6 Leakage to groundwater



Operation losses



Total water supplied


(a) Riparian releases are generally made seasonally from surface water storages and water mains within the Perth region. Part of the surface water diverted for the urban water system (line item 11.12) is released to the environment. For more detail, please see Environmental benefit note.

Assumptions, Limitations, Caveats and Approximations


Uncertainty Information

Expected error for water meters is +/– 5%.

The Department of Water requires that all water meters, when tested in situ conditions, must be within 5% accuracy across the full flow rate range (Guidelines for water meter installation 2009).

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 19.4

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

19.4 Delivery to urban water users

20.3.2 Application of water from urban water supply system for irrigation or outdoor use



Line item classification: line item name, number and definition has changed from the 2010 Account

The scope of this line item has changed in this account from that in the 2010 Account. The scope was changed because of a change in the definition of the region. The 2011 Account considers that all individual users (including commercial and industrial sectors) are not part of the region. Therefore, water delivered to urban users leaves the region and this represents a water asset decrease.

In the 2010 Account, water delivered to urban users was not considered to have left the region. Only water subsequently used for outdoor use (e.g. watering the garden) was considered to have left the region. Therefore, only a portion of the water delivered to urban users represented a water asset decrease. This explains the large difference in the 2009–10 year volume reported in this account compared to that reported in the 2010 Account.