The development of water quality indices for operational management

The derivation, structure and application of a Water Quality Index (WQI) for the classification of surface water quality is discussed and the efficiency of the developed WQI is compared with the standard UK classification system of the National Water Council (NWC). The general WQI is developed through the objective and rigorous selection, transformation and weighting of determinands with rating curves based on legal standards and quality directives or guidelines. Three further indices intended for potable supplies and evaluation of toxicity are also discussed. The utility of the developed index for operational management is demonstrated by a comparative study with the NWC classification for a number of rivers in the Greater London region. The flexibility and advantages of a WQI approach in providing potential cost benefit/assessments for water quality on both temporal and spatial scales are also highlighted.