Perth
19.10 Discharge from urban water system to groundwater

This line item volume (1,714 ML) represents the total volume of treated wastewater infiltrated to groundwater from the Kwinana Wastewater Treatment Plant during the 2012–13 year.

Treated wastewater from the Kwinana treatment plant is infiltrated to the groundwater store to assist in maintaining environmental values at the Spectacles Wetlands on the Swan Coastal Plain. The groundwater in this region is also extracted and recycled by Alcoa as part of the overall allocation of groundwater in the region.

The recycled water 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, approximately 8% of the treated wastewater from the wastewater system is recycled.

During the 2012–13 year, approximately half of the recycled water produced was resold for industrial and municipal use (part of 19.4 Delivery to urban water system users). Approximately 24% of the recycled water was used on-site at the wastewater treatment plants throughout the region; the remaining recycled water was used to recharge aquifers—via injection wells (19.9 Managed aquifer recharge) or infiltration basins (19.10 Discharge from urban water system to groundwater).  The following figure shows all the inflows and outflows associated with the recycled water 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 recycled water system; line item numbers are provided in brackets

Treated wastewater from the Kwinana Wastewater Treatment Plant is infiltrated to the groundwater store via infiltration ponds. The volume of treated wastewater infiltrated to groundwater is based on metered data at the treatment plant that is collected on an almost continuous basis.

It is assumed that the entire volume of treated wastewater discharged to infiltration ponds infiltrates into the groundwater store; however, it is likely that some water may be lost through evaporation.

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).