Sydney
25.1 Unaccounted-for difference
Supporting information
In the Sydney 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. It is calculated according to the following table.
|
Account |
Volume (ML) |
|
Opening water storage (30 June 2012) |
2,780,522 |
add |
Total water inflows |
5,623,657 |
minus |
Total water outflows |
5,421,435 |
minus |
Closing water storage (30 June 2013) |
2,838,384 |
|
Unaccounted-for difference |
144,360 |
The unaccounted-for difference of 144,360 ML represents around 5% of the total water storage for the Sydney region and 2% of the total water inflows. The unaccounted-for difference in the Sydney account found in both the urban water system and the surface water can be attributed to:
- modelling errors, particularly in reference to 9.4 Runoff to surface water and 17.2 River outflow from the region
- uncertainty in estimating leakage (see 19.3 Leakage to groundwater)
- errors in measurement equipment and/or meter accuracy on gauging stations and flow meters.
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 (ML) |
| Balancing item–surface water store | 138,635 |
| Balancing item–urban water system store | 5,725 |
| Unaccounted-for difference |
144,360 |
Detail of the balancing items calculation is given in the following Water resources and systems notes:
- Surface water
- Urban water system
Comparative year
There have been several restatements from the 2012 Account. As a result, the volume stated in this line item has been restated from 208,300 ML (as published in the 2012 Account) to 227,952 ML.