Perth
Future

Table 1 shows that there is a deficit of available water assets over water liabilities and future water commitments that are expected to be settled within 12 months of the reporting date.

^(a)  Inactive storage is part of the accessible volume (see Water storage glossary), but is considered to be the minimum operating volume for storages below which no water is released or abstracted.

The expected diversions and extractions are based on abstractions made during the 2010–11 year. Record low rainfall during the 2010–11 year (see Climate overview) has resulted in lower storage levels across the region compared with previous years. As a consequence, less surface water is available in the region for urban water supply and, therefore, it is likely that surface water allocation for urban water supply will decrease in the 2011–12 year compared with the current year.

Based on recent data (the past 10 years), future inflows to surface water storages in the region are likely to be approximately 100,000 ML. Net groundwater recharge from rainfall is estimated to be between 700,000 and 900,000 ML. Inflow of desalinated water is estimated to be 100,000 ML for the 2011–12 year. Therefore, the deficit of water assets over water liabilities and future water commitments may just be met with the 2011–12 year inflows and recharge.

The total water assets in Table 1 only represents total water in the surface water store at 30 June 2011. Groundwater assets are not included, because the volume of water in aquifers could not be quantified.

The Department of Water sets an extraction limit on the groundwater aquifers within the Perth region. This limit is established to protect groundwater-dependent ecosystems. Only water above this prescribed minimum water table level is recognised as a water asset in the account. The volume of water that is beyond this extraction limit is considered a contingent water asset for aquifers in the Perth region. However, there is currently not enough information available regarding groundwater resources in the region to allow for a volumetric estimate.

Water for urban use (210,000 ML): Water Corporation manages the bore fields and surface water storages used for urban water supply. Water Corporation also maintains water within the urban water system for delivery to the Perth metropolitan area and other urban centres within the Perth region. However, the actual delivery of the water is contingent on when customers use the water. It is estimated that 210,000 ML will need to be delivered in the 2011–12 year (160,000 ML from groundwater stores and 50,000 ML from surface water stores).

Water for irrigation use (30,000 ML): Harvey Water, a private irrigators' cooperative in the Perth region, is required to supply water to its members for irrigation. It is estimated that 30,000 ML will need to be delivered in the 2011–12 year. The amount of water delivered is contingent on the irrigators of the Harvey Water Irrigation Cooperative drawing water from the system.

Water for private use (345,000 ML): Department of Water allocate water to individual users (e.g. mining, industrial or agricultural sectors). However, the actual delivery of the water is contingent on when customers use the water. It is estimated that 345,000 ML will need to be delivered in the 2011–12 year (300,000 ML from groundwater stores and 45,000 ML from surface water stores).