18.8 Entitled extraction of non–allocated groundwater to users
The volume reported in the water accounting statements (65,043 ML) represents the volume of groundwater extracted from domestic non-licensed bores within the Perth region during the 2011–12 year.
The Department of Water does not have sufficient metering information relating to actual extraction from domestic non-licensed bores to determine the total volume of water extracted. Consequently, the extraction was estimated based on ABS survey results (2009) for the Perth metropolitan area. These usage figures in the Perth metropolitan area were then extrapolated to also include the southwest area (around Mandurah). The estimated annual extraction per bore is 0.405 ML per year, which is based on the initial results of the Department of Water's domestic bore metering project for several dozen domestic bores across Perth.
Assumptions, limitations, caveats and approximations
The estimate for domestic non-licensed extraction is based on a number of assumptions, including:
- The ABS domestic bore survey is relevant for the southwest area, for which there is no alternative, independent research or evidence available; and
- The usage based on the Department of Water's research for several dozen bores was used to estimate the usage of all non-licensed bores in the region.
This line item corresponds to line item '18.8 Non–allocated extractions to users' reported in the 2011 Account.