Perth
19.20 Other urban water system decreases

The volume reported in the water accounting statements (8,407 ML) represents all other losses associated with the urban water supply system within the Perth region during the 2012–13 year.

This volume is comprised of two components:

• operational losses from the urban water supply system (588 ML)
• all other non-revenue water from the urban water supply system, such as consumer meter inaccuracies and unauthorised consumption (7,819 ML).

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.

The volume of operational losses in the urban water supply system is based on measured discharge data collected by flow meters installed at the site.

Non-revenue water is water that is lost before it reaches the customer. The total volume of non-revenue water is calculated by subtracting the metered volume of water consumed (revenue water) from the metered volume of water supplied. Part of this non-revenue water is presented in line item 19.3 Urban water system leakage to groundwater. The remaining non-revenue water is calculated as shown in the following table.

¹ Estimated as total water supplied to the users (253,800 ML) minus total water consumption (224,810 ML), as provided in the Water Corporation Annual Report 2013.

Total non-revenue water is not measured but is estimated based on the difference between the metered volume of water supplied and the metered volume of water consumed (revenue water).

This value is estimated to be in the range of +/– 5–10%.