Perth
19.8 Other wastewater discharge

The volume reported in the water accounting statements (5,338 ML) represents the total volume of treated wastewater discharged to infiltration lagoons from wastewater treatment plants within the Perth region during the 2012–13 year.

Total volume of treated wastewater discharged into infiltration lagoons from each treatment plant during the 2012–13 year is 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

The total volume of water discharged into infiltration lagoons based on both measured and estimated data. For wastewater treatment plants where outflow data are available, the volume of discharge to infiltration lagoons is based on metered data collected at the site.

For treatment plants where outflow data are not metered, the volume of discharge to infiltration lagoons is estimated by subtracting the volume of recycled wastewater from the total inflow of water into the treatment plant. Both inflow and recycled volume data are based on measured discharge data collected at the site.

For estimated outflow data, it is assumed that the volume of treated wastewater discharged into infiltration lagoons is simply the total inflow of wastewater into the wastewater treatment plant minus the volume of water recycled.

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