The importance of robustness in drinking-water systems.

It is important that drinking-water systems be as robust as possible. That is, they should deliver excellent quality water under adverse conditions. Robustness is important for each of the five elements that can be considered necessary for providing safe drinking water (a good source, adequate treatment, secure distribution, appropriate monitoring, and appropriate response to adverse monitoring results). However, a given degree of overall system robustness can be achieved in varying ways. The quantification of robustness facilitates its improvement in a rational way. This paper introduces the concept of robustness, and illustrates one way in which it could be quantified by means of an example involving filtration in relation to Cryptosporidium removal. With regard to a serious water contamination incident that occurred in Canada during May 2000, the robustness of each of the five elements (source, treatment, distribution, monitoring, and response) is assessed qualitatively to explain the overall vulnerability of the water-supply system in that town.