Melbourne
19.5 Discharge from urban water system to surface water

The volume presented (12,161 ML) represents the treated wastewater discharged to surface water from South East Water's sewage treatment plants (STPs), Western Water's recycled water plants (RWP) and Yarra Valley Water's local treatment plants (LTPs).

The breakdown of treated wastewater discharge to surface water in the Melbourne region during the 2011–12 year is presented in the following table.

¹ Total volume reported by South East Water (650 ML) is greater than the volume derived from the rounded components (649 ML).

The wastewater system is one of three sub-components of Melbourne's urban water system. The three sub-components are the:

• Urban water supply system
• Wastewater system
• Recycled water system.

In the Melbourne region, wastewater is collected (11.4) from users by the four retail water authorities within the region:

• City West Water
• South East Water
• Western Water
• Yarra Valley Water.

Following collection, wastewater is either delivered to smaller, local wastewater treatment plants operated by the authorities, or, more commonly, delivered to one of Melbourne Water's major wastewater treatment plants: the Eastern Treatment Plant and Western Treatment Plant. During the 2011–12 year Melbourne Water received and treated almost 90% of the wastewater collected within the region. The breakdown of the volumes of wastewater received by Melbourne Water's treatment plants and the authority's smaller treatment plants is presented in the following table.

¹ Includes 1,623 ML of treated wastewater received from Pakenham Sewage Treatment Plant.

During the 2011–12 year the majority (85%: 19.7) of treated wastewater was discharged to sea; approximately 11% was recycled and the remaining portion was discharged to surface water (3%: 19.5 ) and the landscape (<1%: 19.8).

The following figure shows all the inflows and outflows associated with the wastewater system. A small misbalance (> 1%) is shown. The misbalance can be attributed to metering inaccuracies, unaccounted losses and inaccuracies in the estimation of the recycled water on-site in process use.

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 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 for Melbourne's wastewater system during the 2011–12 year. Line item numbers are provided in brackets.

This item represents the daily metered volume of treated wastewater discharged to Deep Creek, Adams Creek, Parrot Creek and Yallock Creek. 

Nil.

Meters are located at the outlet of the treatment plants and are read daily by the treatment plant operators. 

The uncertainty is estimated to be +/– 5% based on meter specifications.

The uncertainty is estimated to be +/– 5% based on meter specifications.