Perth
18.11 Entitled extraction of allocated groundwater to users

The volume recognised in the water accounting statements (274,546 ML) represents the total volume of groundwater extracted for individual user licence entitlements during the 2012–13 year.

This line item refers to all groundwater supply in the Perth region not related to urban water systems or irrigation schemes. It includes water extracted by individual users in the agricultural, industrial and commercial sectors.

The Department of Water does not have sufficient metering information relating to actual extraction from licensed bores to determine the total volume of water extracted. Consequently, the allocation extraction during the year is estimated based on the licensed allocation.

The volume of abstraction is estimated to be the full allocation, divided by the number of days that each licence was active during the 2012–13 year. The number of days the licences were active is calculated using the issue date of each individual licence.

• For licences that expired and were renewed during the 2012–13 year, the volume of abstraction is estimated to be the full licensed allocation.
• For licences that expired during the 2012–13 year (and were not renewed), the volume of abstraction is estimated to be the full allocation, divided by the number of days from 1 July 2012 until its expiry date.
• For new licences that were created during the 2012–13 year, the volume of abstraction is estimated to be the full allocation, divided by the number of days from the licence issue date until 30 June 2013.

Some licences are issued in perpetuity and do not have a finalisation date. In these cases, the volume of abstraction is estimated as the amount of one full year's allocation for licences in force during the 2012–13 year.

There is not sufficient information relating to actual abstraction to provide more accurate estimates of abstraction for all licences. The pro-rata estimates of abstraction assume that the full annual allocation is abstracted each year, and that the rate of abstraction is uniform throughout the year. It is unlikely on both counts that this will be the case for all licences.

The volume of extraction of allocated groundwater for the 2011–12 year has changed from that presented in the 2012 Account. Please refer to Restatement of comparative information in the 'Water accounting policies' for more information.