Perth
19.4 Delivery to urban water system users

The volume reported in the water accounting statements (237,896 ML) represents the total volume of water delivered to urban water system users within the Perth region during the 2011–12 year.

This volume is comprised of two components:

• water supply to users from the urban water supply system (232,602 ML)
• water supply to users from the recycled water system (5,294 ML).

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

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

Almost 98% of the water delivered to urban water users during the 2011–12 year came from the urban water supply system (232,602 ML).

During the 2011–12 year, approximately 73% of the urban water supply system outflow was water supply to urban users (232,602 ML). Approximately 20% of the urban water was transferred back to surface water storages (part of 19.5). The majority of this water was transferred for the storage of desalinated water produced during winter and to balance the storages in preparation for peak summer supply. 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 2011–12 year for Perth's urban water supply system. Line item numbers are provided in brackets.

Approximately 2% of water delivered to urban water users came from the recycled water system (5,294 ML).

During the 2011-12 year, approximately 49% of the recycled water produced was delivered to urban users, primarily for industrial use and local irrigation (e.g. parks and recreation grounds). Approximately 24% of the recycled water was used on-site at wastewater treatment plants throughout the region; the remaining 27% was used to recharge aquifers—via injection wells (19.9) or groundwater infiltration (19.10).  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 recycled water 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 during the 2011–12 year for Perth's recycled water system. Line item numbers are provided in brackets.

Total volume of treated wastewater recycled for further use from each treatment plant during the 2011–12 year is given in the following table.

During the 2011–12 year, the volume of treated wastewater recycled for further use was equivalent to approximately 4% of the total treated wastewater discharged from treatment plants within the region.

Total water supply to urban users within the Perth region from the urban water supply system during the 2011–12 year is calculated as shown in the following table.

The volume of recycled water supplied to users is based on measured discharge data collected by flow meters installed at the wastewater treatment plant.

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 (Guidelines for water meter installation 2009).

In the 2011 Account, the delivery of recycled water to users from the recycled water system was not included in the total volume of this line item. Instead, the delivery of recycled water to users was included in line item '19.20 Other urban water system decreases'. This was an error in the 2011 Account.

In the 2012 Account, the volume of recycled water supplied to users is included in the total volume of water delivered to urban water system users. Consequently, the comparative year value has been restated in the water accounting statements from 238,273 ML (as published in the 2011 Account) to 243,724 ML.

The comparative year value for line item 19.20 Other urban water system decreases has also been restated in the 2012 Account.