19.20 Other urban water system decreases
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 (1,148 ML) represents the operational losses associated with the urban water supply system within the Perth region during the 2011–12 year.
The volume of water losses in the urban water supply system is based on measured discharge data collected by flow meters installed at the wastewater treatment plant.
Assumptions, limitations, caveats and approximations
This value is estimated to be in the range of +/– 5–10%.
This line item corresponds to line item '19.20 Other urban water decreases' reported in the 2011 Account.
In the 2011 Account, operational losses from the urban water system were not included in the account. Instead, this line item was assumed to represent the volume of recycled water supplied to users. This was an error in the 2011 Account.
In the 2012 Account, this line item refers to operational losses from the urban water system. The volume of recycled water supplied to users from the recycled water system is included in line item 19.4 Delivery to urban water system users. Consequently, the comparative year value was restated in the water accounting statements from 7,234 ML (as published in the 2011 Account) to 1,136 ML.