Catchment characterisation and source water quality

Abstract

The first, and a key, step in providing safe drinking water is the selection of the best available source water. The most protected source waters will be the easiest and the cheapest to transform into safe drinking water. This is a general principle, and is one that has been known since the times of Plato (Whitlock, 1954 ). The Romans, for example, abandoned the river Tiber as a drinking water source in the third century BC and built 14 aqueducts in order to bring clean water from the surrounding hills. Principle, however, is not always translated into practice, although such oversights can have dramatic results, with a good example being provided by the Milwaukee <em>Cryptosporidium</em> outbreak (MacKenzie <em>et al.</em>, 1994), which occurred in the spring of 1993 and was<br />estimated to have caused illness in 400 000 people. The intake of Milwaukee's Howard A venue drinking water treatment plant was located at a site in Lake Michigan that directly received the discharge of the Milwaukee River. The city's sewage treatment plant discharged into the Milwaukee River just upstream of the river mouth. Unsurprisingly, this made the intake of the plant vulnerable to fresh faecal contamination, especially during storm events. A study in the 1960's had already shown that this lake area contained high levels of faecal pollution (Schoenen, 2001). If this information had been used to select a more appropriate location for the intake point, or to redirect the sewage discharge, the contamination level during spring 1993 would very likely have been significantly lower and perhaps a major outbreak would have been avoided. [...]