Perth
19.1 Evaporation from urban water system

The volume reported in the water accounting statements (89 ML) represents the total volume of evaporation losses from wastewater treatment ponds in Perth's urban water system during the 2012–13 year.

Total evaporation losses from each treatment plant during the 2012–13 year are given in the following table.

The wastewater 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.

In the Perth region, wastewater is collected from users by the Water Corporation (11.4 Wastewater collected) and transferred to wastewater treatment plants throughout the region.

During the 2012–13 year, approximately 8% of treated wastewater was recycled; 88% discharged to the sea (19.7 Wastewater discharge outside of region); and the rest discharged to rivers (part of 19.5 Discharge from urban water system to surface water) or infiltration lagoons (19.8 Other wastewater discharge). The following figure shows all the inflows and outflows associated with the wastewater system.

For more detail on a particular flow associated with the wastewater system, refer to the line item notes. Volumes in the figure annotated with an asterisk (*) indicate flows between urban subcomponents and are not reported in the account. As such, these flows do not have an associated line item number or note.

Schematic diagram of water inflows and outflows during the 2012–13 year for Perth's wastewater system; line item numbers are provided in brackets

Operational Data Storage System.

The total volume of water that evaporates from the wastewater treatment ponds is not measured. The volume is estimated as total inflow of wastewater into the treatment plant minus the volume of outflow.

Prior to the 2012–13 year the volume of evaporation from the urban water system was not estimated.

It is assumed that all losses from the wastewater system are evaporation losses from the wastewater treatment ponds.

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