Perth
11.6 Delivery of desalinated water to urban water system
Supporting information
a. Supporting information
The volume reported in the water accounting statements (95,770 ML) represents the total volume of desalinated water supplied to the urban water system within the Perth region during the 2012–13 year.
There are two desalination plants that supply water to the Perth metropolitan area. The volume of water supplied to the region from each desalination plant during the 2012–13 year is given in the table below.
Desalination plant |
Water supplied (ML) |
Perth Seawater |
48,370 |
Southern Seawater |
47,400 |
Total |
95,770 |
According to the figure above, desalinated water made up almost 30% of the urban supply water during the 2012–13 year; last year the contribution of desalinated water was 78,847 ML (approximately 25% of the urban water supply).
b. Urban water supply system overview
The urban water supply system is one of three subcomponents of Perth's urban water system. The three subcomponents are the:
- urban water supply system
- wastewater system
- recycled water system.
There are three main sources of water for Perth's urban water supply system:
- surface water (11.12 Entitled diversion of allocated surface water to urban water system)
- groundwater (11.13 Entitled extraction of allocated groundwater to urban water system)
- desalinated water (11.6 Delivery of desalinated water to urban water system).
Urban water consumption (part of 19.4 Delivery to urban water system users) was 224,810 ML during the 2012–13 year, representing approximately 69% of all urban water supply system outflows. Approximately 22% of the urban water supply system outflows was transferred back to surface water storages (part of 19.5 Discharge from urban water system to surface water). The majority of this water was internal transfers for the storage of desalinated water produced during winter and to balance the storages in preparation for peak summer supply. Less than 1% of the urban water supply system outflow was transferred to Western Australia's southwest region (19.11 Transfer of water outside of region); the remaining outflow was lost through leakage to groundwater (19.3 Urban water system leakage to groundwater) and operational losses (19.20 Other urban water system decreases).
The following figure shows all the inflows and outflows associated with the urban water supply system. For more detail on a particular flow associated with the urban water supply system, refer to the line item notes.

Schematic diagram of water inflows and outflows during the 2012–13 year for Perth's urban water supply system; line item numbers are provided in brackets
Quantification approach
Data source
Provided by
Method
Total desalinated water used for urban water supply is based on measured outflow data at the Perth Seawater Desalination Plant, located in Kwinana, and the Southern Seawater Desalination Plant, located near Binningup.
Assumptions, limitations, caveats and approximations
It is assumed that all desalinated water is supplied directly to the urban water supply system. Some desalinated water is transferred to surface water storages prior to consumption by urban water users. This water is included in line item 19.5 Discharge from urban water system to surface water.
Uncertainty information
Expected error for water meters is +/– 5%.
The Department of Water requires that all water meters, when tested under in situ conditions, must be within 5% accuracy across the full flow rate range (Department of Water 2009c).