Improvement of the representation of water quality by application of information theory

The quality of surface waters depends on chemical, physical and biological properties. An official definition of normal values of various chemical constituents for the construction of a classification scale of water quality has been in use for some years; water quality of each sampling location is presented on geographical maps by colour codes. The information content of these maps has decreased considerably in recnet years, because of improving water quality. In the method described here, a different selection of class boundaries is used, so that all classes are well populated, and data are weighted to emphasize extreme situations. This improves the information content of the maps, simplifying choices of locations for remedial action.