In 2005, 99.5% of water abstracted was from freshwater sources, with the balance coming from seawater desalination or wastewater reuse. Surface water provided the majority of the water resource, but 36% came from groundwater sources. Groundwater is under increasing threat since it is effectively a non-renewable source, taking millennia to accumulate, but just a few years or decades to deplete. Also, groundwater is deteriorating in quality due to human activity, becoming polluted from agricultural residuals, and in some areas by saline intrusion.
The development of new resources is therefore critical. Ultimately, alternative resources will need to displace a significant proportion of groundwater sources. Indeed, it is predicted that reuse levels of 20% or 30% will become common for many developed areas and that water scarce areas may need to provide more than 70% of their water resource from alternative sources.