Canberra
19.5 Discharge from urban water system to surface water

The volume reported in the water accounting statements is 31,702 ML that represents the total volume of water discharged from the urban water system to surface water within the Canberra region during the 2012–13 year.

This volume is comprised of two components:

• discharge to surface water from the urban water supply system
• discharge to surface water from the wastewater system.

When capacity is available, treated water is transferred from Mount Stromlo Water Treatment Plant (WTP) into Googong Reservoir via the ACTEW Water water reticulation network. In addition to this there are three sewage treatment plants (STPs) within the Canberra region.  The Lower Molonglo Water Quality Control Centre (LMWQCC) discharges treated water into the Molonglo River at the upstream of the confluence with the Murrumbidgee River. The Queanbeyan STP discharges into the Molonglo River and the Uriarra STP discharges into Tarpaulin Creek and drains into the Murrumbidgee River.

The table below contains a breakdown of the volume of water discharge to surface water at each sewage treatment plant and the volume of water transferred to the Googong Reservoir.

Canberra's urban water system comprises three sub-components:

• urban water supply system
• wastewater system
• recycled water system.

Less than 1% of the urban water discharged to surface water during the 2012–13 year came from the urban water supply system. That is the transfer of 66 ML from Bendora and Cotter reservoirs to Googong Reservoir.

During the 2012–13 year, approximately 91% of the urban water supply system outflow, 43,754 ML was water supply to urban users (part of 19.4). The remaining urban water was lost through leakage to groundwater (19.3) and operational losses (19.20).

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 Canberra's urban water supply system. Line item numbers are provided in brackets

The treated wastewater volume discharged to surface water after treatment was 31,636 ML, approximately 77% of the total treated wastewater volume, 41,114 ML.

During the 2012–13 year, approximately 12% of treated wastewater was recycled; the rest was the losses. The following figure shows all the inflows and outflows associated with the wastewater system.

For more detail on a particular flow associated with the recycled water system, refer to the line item notes. Note that volumes annotated with an * indicate flows between sub-components and are not reported in the account. As such, these flows do not have an associated line item number.

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

The volume 28,998 ML is the total wastewater discharge from LMWQCC measured at the discharge point plus the volume of effluent discharged from Uriarra STP.  The volume discharged is measured using level sensing and flow measuring equipment.

Nil.

Derived from measured data. Estimated uncertainty is +/– 5%.

ACTEW Water's flow meter measures the release from the water distribution system to Googong Reservoir. The metered volume of this release for 2012-13 was 66 ML.

Nil.

Derived from measured data. Estimated uncertainty is +/– 5%.

The volume of treated wastewater discharged to the surface water system 2,638 ML was derived from the daily measured values of wastewater discharged to surface water at the Queanbeyan STP.  The Queanbeyan STP is the only QCC STP that discharges treated wastewater to the surface water system.

Nil.

Derived from measured data. Estimated uncertainty is +/– 5%.