A better water quality indexing system for rivers and streams

The development of a better system for indexing water quality and its application to four water use classes are described. There are three dominant use classes: bathing, water supply, and fish spawning, and one general use class. In all of them protection of aquatic life is included. To ensure that the index score tells us something useful and does not hide important information as current indexes (or indices) tend to do, the water quality variable giving the lowest score (i.e. the minimum operator) has been employed to produce the final index score. Preliminary indications are that this is a more useful aggregation method than the more commonly used additive, and multiplicative techniques. Index development has been linked to recommended water quality standards developed for New Zealand water legislation. The indexes are intended to assist in the dissemination of water quality information, particularly to lay-people.