The desirability of developing water quality indices, which has been frequently cited, is examined. The development of currently available indexes are reviewed and a distinction is made between the indexing and scoring of water quality samples. It is pointed out that many indexes are, in fact, scoring methods, and that the mathematical basis for the scoring methods are not always consistent with the objectives of scoring. A general mathematical approach to scoring is described, and the necessity of considering the uniformity as well as the average quality of the water is described. The development and use of true indices is briefly reviewed and recommendations for future indexing approaches are presented.