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The volume recognised in the water accounting statements (6,276 ML) represents the volume of groundwater extracted during 2009–10 by self-supply licencees, excluding extraction for the purpose of urban water supply.

The breakdown of groundwater abstraction according to the stated licence entitlement purpose is provided in the table below.

Data source

Western Australian Department of Water: Water Resource Licensing (WRL) database and the Water Information (WIN) database.

Data provider

Western Australian Department of Water.

Method

The volume presented for this line item is a combination of metered data and estimates.

Where metered data are available, the abstraction is calculated as the actual extraction for the reporting period. Where metered data are not available, the volume of extraction is estimated to be the full annual entitlement, divided by the number of days that each licence was active during the reporting period. The number of days the licences were active is calculated using the annual renewal date of each individual licence:

• for licences that expired during the reporting year, the volume of extraction is estimated to be the full entitlement, divided by the number of days from 1 July 2009 until its expiry date
• for new licences that were created during the reporting year, the volume of extraction is estimated to be the full entitlement, divided by the number of days from the licence start date until 30 June 2010.

Some licences are issued in perpetuity and do not have an annual renewal date. In these cases, the volume of extraction is estimated to be as the amount of one full year’s allocation for licences in force during the reporting year.

Uncertainty

Derived from estimated data. Ungraded.
Derived from measured data. Uncertainty range +/–5%.

Assumptions, approximations and caveats/limitations

• There is not sufficient information relating to actual extraction to provide more accurate estimates of extraction for all licences. The pro-rata estimates of extraction assume that the full annual entitlement is extracted each year and that the rate of extraction is uniform throughout the year. It is unlikely on both counts that this will be the case for
  all licences.
• For licences that are metered, the licencee is required to install a cumulative water meter of a type approved under the Rights in Water and Irrigation (Approved Meters) Order 2009 for each water draw point under the licence. The licencee must ensure the installed meter(s) accuracy is maintained to within +/–5% of the volume metered, in
  field conditions.
• Meters must be installed in accordance with the provisions of the Guidelines for Water Meter Installation (Western Australian Department of Water 2009).