Perth
Future outlook

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.

1. 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 2011–12 year. However, it is likely that there will be less dependence on surface water and groundwater resources for urban water supply in the 2012–13 year. Due to recent trends of declining inflows into surface water and groundwater stores, desalinated water has become increasingly important for the region. The second stage of the Southern Seawater Desalination Plant was commissioned in January 2013, which will mean desalinated water will provide almost half the urban water needed for the region during the 2012–13 year.

The deficit of water assets is likely to be met by storage inflows and groundwater recharge. Based on recent data (collected over the past ten 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 800,000 and 1,000,000 ML.

The total water assets in Table 1 only represents total water in the surface water store at 30 June 2012. Groundwater assets are not included because the volume of water in aquifers could not be quantified (see Groundwater section of the 'Water resources and systems' note).

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): The Water Corporation manages the bore fields and surface water storages used for urban water supply. The 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 2012–13 year (160,000 ML from groundwater stores and 50,000 ML from surface water stores).

Water for irrigation use (30,000 ML): The Harvey Water Irrigation Cooperative is required to supply water to its members for irrigation. It is estimated that 30,000 ML will need to be delivered in the 2012–13 year. The amount of water delivered is contingent on the irrigators of the cooperative drawing water from the system.

Water for private use (325,000 ML): The 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 325,000 ML will need to be delivered in the 2012–13 year (300,000 ML from groundwater stores and 25,000 ML from surface water stores).