Capital cities summary

Capital city water balance area definition

The capital and major city water supplies generally involve linking up catchments to harness adequate water supplies. For AWR 2005, there was considerable discussion on what the appropriate boundaries for the capital city water balances should have been. Historically, the boundaries for water balances have been based on the urban footprint and or the area serviced by the urban water authority. However this creates a water supply balance rather than an actual water cycle balance.

The area definition chosen was a combined approach, where those water management areas that intersected with the capital city urban footprint collectively defined the reporting boundary. This meant that the boundary did not necessarily include all supply or discharge areas. This is why most of the capital city balances have a transfer in from other entities, and also have transfers or flows out of entity as the discharge/ outfalls from the city are not wholly included in the defined water balance area. The other reason for the use of this boundary was so that future assessments are based on a consistent boundary not defined by water authority boundaries which may change.

Maps of the areas for AWR 2005 water balances are available in the Regional Water Resources Assessments section.

Capital city water balance key findings

Summary of the capital city water balances components (volumes in GL)

na applies where data was not available on that component of the water balance

For assessment of the water balances for capital cities consideration should be given to the impact of low rainfall and water demand measures that were in place to control water use. Only Hobart and Darwin were not limiting demand by use of restrictions and or permanent water restrictions.

Water storage levels in Sydney, Brisbane and Melbourne were all below 50% of capacity and have fallen further since July 2005.

Alternative water supplies in capital cities

Nearly 1000 GL of treated wastewater was discharged to the ocean in 2004-05. This is a significant volume, that with the pressures of reduced rainfall is likely to drive the use of alternative water supplies, such as aquifer storage and recovery (ASR), rainwater tanks, and effluent re-use. With respect to alternative water supplies, if the objective is to enhance the efficiency and effectiveness of water supply systems, the emphasis in effluent re-use may need to be on potable water substitution, rather than land disposal schemes.

Aquifer storage and recovery (ASR) also known as managed aquifer recharge (MAR) has significant potential for managing alternative water sources, and or improving the delivery of current water supplies. The National Water Commission is currently reviewing related proposals that will assist in the uptake of these technologies.

Rainwater tanks are increasing in usage across major cities and in other urbanised areas reducing the demand for mains water supply for non-potable uses such as garden watering and toilet flushing. Government rebates for water tanks are helping to advance the installation of rainwater tanks.

Desalinisation is another potential area for increasing water supplies in the future. Perth has recently commissioned a seawater desalination plant, Gold Coast is expected to do so shortly and Sydney and Melbourne are considering proposals to build plants to relieve demand on current supplies of freshwater.

Future use of water balances for capital cities

If the main objective for the water balance for a capital city it is to primarily assess the opportunities for water savings and improved recycling or alternate water sources, a simpler balance with more detail on these items may be more useful than the water cycle approach used for AWR 2005. More detail on the actual drainage volumes (stormwater run-off) which was limited in availability would also be informative. Once the objective is clarified the water balance can then be tailored for the appropriate entity and time period to be reported on (e.g. monthly balances for the whole year).

What is clear is that the aim and objectives of assessing a water balance for each capital city differs from the rural areas. There are different issues in terms of resource sustainability, and an increased ability to use alternative sources (effluent recycling, stormwater harvesting, seawater desalinisation, etc.) due to the high demand. Future assessments of capital cities should include additional information on effluent re-cycling to determine how much is used within the treatment process and how much is available for other uses (e.g. as an alternate source for irrigation or drinking water). This data was either not collated or not available as part of the AWR 2005 assessment.

Further discussion of the water balance results for capital cities is provided in the Water Availability National Perspective report, and the Regional Water Balances report, which are both available on the Publications page.

For individual results of water balance assessments go to Regional Water Resources Assessments

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