Perth
19.7 Wastewater discharge outside of region

The wastewater system is one of three sub-components of Perth's urban water system. The three sub-components 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) and transferred to wastewater treatment plants throughout the region.

During the 2011–12 year, 8% of treated wastewater was recycled; 88% discharged to the sea (19.7); and the rest discharged to rivers (part of 19.5) or infiltration lagoons (19.8). 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. Note that volumes annotated with a * indicate flows between urban sub-components 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 2011–12 year for Perth's wastewater system. Line item numbers are provided in brackets.

The volume reported in the water accounting statements (118,952 ML) represents the total volume of treated wastewater discharged to the sea from wastewater treatment plants within the Perth region during the 2011–12 year.

Total volume of treated wastewater discharged to the sea from each treatment plant during the 2011–12 year is given in the following table.

The total volume of wastewater discharged into the sea is not metered and is estimated as total inflow of wastewater into the treatment plant minus the volume of water recycled.

Outflows from these treatment plants are not measured. It is assumed that the volume of wastewater discharged into the sea is simply the total inflow of wastewater into the treatment plant minus the volume of water recycled and there are no other losses.

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