Foster et al. (1998) highlight the provision of water supply, sanitation and drainage as a key requirement of the urbanisation process, with the subsurface playing an important role in all three of these elements, and in the disposal of industrial effluent and solid waste. This is illustrated by Figure 2.1. The subsurface is therefore a key consideration, and the presence of permeable subsoil and shallow groundwater are critical factors. As groundwater is generally of high natural quality, and a more constant source than seasonally affected surface waters, it is often the first resource to be exploited by overlying cities (Foster et al., 1998), and is shown by Figure 2.2.