Perth
11.12 Entitled diversion of allocated surface water to urban water system

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:

• Surface water (11.12)
• Groundwater (11.13)
• Desalinated water (11.6).

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.

This line item volume (81,553 ML) represents the total surface water diverted for urban water supply in the Perth region during the 2011–12 year.

Total volume of water diverted from each surface water resource to the urban water system during the 2011–12 year is given in the following table.

According to the figure above, surface water made up approximately 25% of the inflows to the urban water supply system during the 2011–12 year. During the comparison year, surface water diverted to the urban water system was 115,629 ML, approximately 35% of the urban supply water (see Urban water system section of the 'Water resources and systems' note).

Total water abstracted from surface water storages for urban water supply within the Perth region is equal to the total annual water released from the storages during the 2011–12 year. The water volumes released from the storages are metered at the outlet continuously and reported on a monthly basis.

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).

This line item corresponds to line item '11.12 Allocation diversion of surface water to urban water system' reported in the 2011 Account.