Perth
19.5 Urban water discharge to surface water

Volume of water transferred to surface water storages from the urban water system during the 2010–11 year is given in the following table. The water transferred from the urban water system is a combination of surface water, groundwater and desalinated water. These internal water transfers occur in order to store winter production of desalination water and groundwater and to balance the storages to prevent overflow and enable summer peak supply capacity.

(a)  Water transfer is direct to Victoria Reservoir and via Bickley Pumpback Reservoir.

Volume of treated wastewater discharged from wastewater treatment plants into rivers during the 2010–11 year is given in the following table.

Volume of water transferred to surface water storages from each pumpback reservoir during the 2010–11 year is given in the following table. Water is collected in these pumpback reservoirs on an opportunistic basis and transferred back to the main surface water storage in order to settle (i.e. reduce turbidity) and become part of the water supply source for that storage.

The volume of water transferred from the urban water system to surface water storages is based on measured inflow data at the storages.

The volume of water discharged to rivers from the Williams, Waroona and Harvey Treatment Plants are based on measured discharge data collected by flow meters installed at the sites.

Expected error for water meters is +/– 5%.

The Department of Water requires that all water meters, when tested in situ conditions, must be within 5% accuracy across the full flow rate range (Guidelines for water meter installation 2009).

The following table presents substantive changes in the line item reported in this 2011 Account with the corresponding line item in the 2010 Account.