Water quality objectives, discharge standards and fuzzy logic

Optimal allocation of water resources requires an agreed basis for discussing what is an "acceptable" water quality. Developments in the establishment and interpretation of water quality specifications are discussed. It is argued that percentile water quality standards and sensible definitions of water quality failure are often inconsistent. Rigid water quality specifications cannot account for complex and ill-defined pollutant interactions and conflicting water use objectives, but need to be qualified by linguistic statements. The use of fuzzy set theory is explored in relation to both the formulation and the interpretation of water quality specifications.