Perth
19.11 Transfer of water outside of region

The volume reported in the water accounting statements (1,259 ML) represents the total volume of water transferred to Western Australia's southwest region, located outside of the Perth region boundary, from Perth's urban water system during the 2012–13 year.

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

Water Corporation Annual Report 2013.

Water Corporation.

The volume of water transferred from Perth's urban water system to Western Australia's southwest region is measured on an almost continuous basis by flow meters installed at the urban water supply system.

Prior to the 2012–13 year the volume of water transferred outside of the region was not reported in the account.

Nil.

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).