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

This line item volume (91,792 ML) represents the total surface water diverted for urban water supply in the Perth region during the 2012–13 year.

Total volume of water diverted from each surface water resource to the urban water system during the 2012–13 year is given in the following table.

According to the figure above, surface water made up approximately 28% of the inflows to the urban water supply system during the 2012–13 year, which is similar to the previous year's contribution of 81,553 ML (approximately 26% of the urban water supply).

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

Operational Data Storage System and the Water Corporation Annual Report 2013.

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 year. The water volumes released from the storages are metered at the outlet continuously and reported on a monthly basis.

The volume of water diverted from the Murray River for supply to Dwellingup was not measured during the 2012–13 year. The total water allocation for Dwellingup is 167 ML (see line item 21.2 Surface water allocation announcements – urban water system); therefore, it is likely that the reported volume of surface water diverted to the urban water supply system is slightly underestimated.

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).