The unaccounted-for difference is the difference between total groundwater outflows (including groundwater extractions) and total groundwater inflows measured during 2009–10, as shown in the following table.
| Account | Volume (ML) | |
|---|---|---|
| Opening balance groundwater store (as at 01 July 2009) | – | |
| add | Total 15 Groundwater inflows | – |
| minus | Total 16 Groundwater outflows | 890 |
| minus | Closing balance groundwater store (as at 30 June 2010) | – |
| Unaccounted-for difference | –890 |
– = no balance available
Because the volume of water in the groundwater stores within the Canberra region could not be quantified accurately due to the lack of data, the volume disclosed in the unaccounted-for difference (–890 ML) represents the change in the groundwater store that has been able to be quantified throughout the reporting period.
This change is based on an estimate of usage using groundwater licence and bore information from the NSW Office of Water and ACT Department of Environment, Climate Change, Energy and Water (See Line item 16.4.1 and Line item 16.4.2).