The Sydney Region’s Statement of Changes in Water Assets and Water Liabilities shows an unaccounted volume of 30,648 ML for the connected surface water store for 2009–10 (1.8% of the total water assets). This volume is the amount required to reconcile inflow volumes against the volume in the connected surface water store.
Possible reasons for this unaccounted volume are:
In estimating outflows to sea, run-off losses in unregulated and ungauged areas resulting from water retaining measures (e.g. rainwater tanks) by urban residents were disregarded. For riparian right and other lumped right holders, water use was estimated by applying 40% of the entitlement-use factor, based on a sample survey.