The net available water is then compared to the total water
demand or use in the locale. If the water demand or use is greater
than the amount supplied, then the WSF is larger than the
catchment’s current water supply capability. Beyond uncertainty
and errors in the measurement of precipitation and evaporation,
there are several ways that this situation can occur in the shortterm.
The first possibility is that groundwater is being extracted
at a greater rate than it is being recharged. A second possibility is
that water is being imported via pipeline or other transport
systems from other areas. Thirdly, there may be additional supplies
of water, such as desalination or recycling. When it comes to
desalination, virtual freshwater demand has to be taken into
consideration: Desalination is an energy intensive process with its
own embedded energy and virtual water needs depending on
production technologies and energy sources. In South-East
Queensland, this is likely to involve electricity from coal-fired
power plants. These power plants have a high associated water
demand. Increasing the energy demand for desalination, therefore,
also increases the freshwater needs of the energy sector. This has
to be included in water supply planning.