Sydney
19.1 Evaporation from urban water system

The wastewater system is one of three subcomponents of Sydney's urban water system. The three subcomponents are the:

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

The Sydney region has several urban utilities responsible for managing wastewater in the region. Sydney Water Corporation, Shoalhaven City Council, Goulburn Mulwaree Council, Lithgow City Council, and Wingecarribee Shire Council all collect wastewater from users (11.4 Wastewater collected) and treat this wastewater at a number of wastewater treatment plants throughout the region.

During the 2012–13 year, a total of 507,638 ML was collected by the wastewater system. The majority of the outflow from the wastewater system (around 77%) was discharged to the sea (19.7 Wastewater discharge outside of region); around 10% was discharged to inland surface water (19.5 Urban water discharge to surface water) and a further 10% of that wastewater was recycled and the remainder was losses from the system (see 19.1 Evaporation from urban water system and 19.20 Other urban water decreases). 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 an asterisk (*) indicate flows between subcomponents 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 Sydney's wastewater system; line item numbers are provided in brackets

The volume of 350 ML in this line item represents the volume of water reported as evaporation from the urban water system by Goulburn Mulwaree Council.

This volume was not reported for the 2011–12 year.

Goulburn Mulwaree Council databases.

Goulburn Mulwaree Council.

Evaporation from storages is not directly measured by Goulburn Mulwaree Council but as there are a number of storages that contain effluent throughout the year evaporation is assumed to occur.

The calculation of evaporation from the storages is described in the table below.

Calculation of evaporation from urban storages in the 2012–13 year

	Item	Volume (ML)
	Wastewater collected (see 11.4 Wastewater collected)	1,788
less	Volume recycled (see 19.4 Delivery to urban water system users)	1,404
less	Discharged to the stormwater on Clinton Street from Goulburn wastewater treatment plant (see 19.5 Urban water discharge to surface water)	34
equals	Loss due to evaporation	350

Evaporation is assumed to be the difference of inflows versus outflows for Goulburn Mulwaree Council.

The volume is based on measured data and estimations. Estimated uncertainty based on meter accuracy and professional judgement is +/– 10%.