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When considering the evolution of the groundwater system in a city, or comparing present-day systems in developing cities with those in more established cities, continually advancing technologies and changing social systems mean that the key to the future does not necessarily lie in the past. This is not to say that history is not fundamental to understanding present-day groundwater flow and quality in a given urban aquifer: each urban system is unique – not just because every aquifer has a different physico-chemical composition, but because of the unique history of impacts that heavily concentrated human activity has on the underlying aquifer.

Usually little is known of the composition or properties of made ground at any given site. Characterization is difficult given the degree of heterogeneity, and geophysical methods of investigation which might otherwise be of considerable use are often rendered impracticable because of paved surfaces, the presence of services and metal objects within the made ground. The same problems can also reduce the utility of geophysical methods for investigating the aquifer below made ground. Sometimes, however, site investigation borehole data may be available from previous construction work.

Surface water infiltration: Where surface water bodies are polluted, there is a risk that pollution will enter the aquifer. g. Smith, 2005). g. Ellis and Rivett, 2006). 3 may result in significant changes to the relationship between surface water components and baseflow: the greater ‘flashiness’ of river flows can mean reduced dilution of baseflow during low flow periods in some systems. Industrial discharges: Industrial discharges may vary widely in composition, many of which will not be found in other contexts.