25.1 Unaccounted–for difference

Supporting information

In the Canberra region, the unaccounted–for difference is the volume necessary to reconcile the opening water storage and closing water storage with the total water inflows and total water outflows reported in the water accounting statements. The unaccounted–for difference is 53,835 ML for the 2011–12 year as shown in the following table:

Calculation of the unaccounted–for difference for the 2011–12 year



Volume (ML)


Opening water storage (30 June 2011)



Total water inflows



Total water outflows



Closing water storage (30 June 2012)



Unaccounted–for difference


The unaccounted–for difference can also be calculated by summing the volumes necessary to reconcile (balance) the opening and closing storage with the water inflows and outflows of each of the separate water stores of the region, as shown in the following table.


Balancing item volume for the Canberra region for the 2011–12 year
Balancing item Volume (ML)
Balancing item–surface water store 52,497
Balancing item–groundwater store 2,136
Balancing item–urban water system store (798)
Unaccounted–for difference 53,835

Detail of the balancing items calculation is given in the following Water resources and systems note:

  • Surface water note (Table 4)
  • Groundwater note (Table 8)
  • Urban system note (Table12)

The second table above shows that the unaccounted–for difference volume is primarily explained by the balancing item of the surface water store. This may be due to an under estimation of outflows from the region following flood events, water leaving the channels and not returning or an over estimation of rainfall runoff from the region.