11.6 Delivery of desalinated water to urban water system
a. Urban water supply system overview
The urban water supply system is one of three sub-components of Perth's urban water system. The three sub-components 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:
Urban water consumption (part of 19.4) was 232,602 ML during the 2011–12 year, representing approximately 73% of all urban water supply system outflows. Approximately 20% of the urban water was transferred back to surface water storages (part of 19.5). The majority of this water was transferred for the storage of desalinated water produced during winter and to balance the storages in preparation for peak summer supply. The remaining urban water was lost through leakage to groundwater (19.3) and operational losses (19.20).
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 2011–12 year for Perth's urban water supply system. Line item numbers are provided in brackets.
b. Supporting information
The volume reported in the water accounting statements (78,847 ML) represents the total volume of desalinated water supplied to the urban water system within the Perth region during the 2011–12 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 2011–12 year is given in the table below.
According to the figure above, desalinated water made up 25% of the urban supply water during the 2011–12 year, an increase from 16% contribution made during the comparison year.
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; however, desalinated water may be stored in surface water storages prior to transfer into the urban water system.
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 (Guidelines for water meter installation 2009).