Describing Water Quality with Aggregate Index

Alternative efforts to describe water quality by an aggregate index consisting of subindices of the constituent quality variables are examined. Ambiguity problems exist where all the subindices are acceptable and yet the overall index is not. Eclipsing problems exist where the overall index is insensitive to a single variable; such insensitivity is unacceptable. A mathematical formulation is developed that avoids these problems of ambiguity and eclipsing. Furthermore, the recommended index form is open to increasing the number of variables included within the index.