A review of water quality index models and their use for assessing surface water quality

• Published in: Ecological indicators Vol. 122; p. 107218
• Main Authors: Uddin, Md. Galal, Nash, Stephen, Olbert, Agnieszka I.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-03-2021; Elsevier
• Subjects: Aggregation function; Model uncertainty and sensitivity; Sub-index; Surface water quality; water quality index (WQI); Water quality parameters; water quality index (WQI); Surface water quality; Model uncertainty and sensitivity; Sub-index; Aggregation function; Water quality parameters
• ISSN: 1470-160X; 1872-7034
• DOI: 10.1016/j.ecolind.2020.107218

•Twenty-one different WQI models were identified and reviewed.•Rivers are by far the most common application of WQI models.•Most models comprised of four key components, the specifics of which varied significantly.•Uncertainty and eclipsing problems are key issues affecting model accuracy.
The water quality index (WQI) model is a popular tool for evaluating surface water quality. It uses aggregation techniques that allow conversion of extensive water quality data into a single value or index. Globally, the WQI model has been applied to evaluate water quality (surface water and groundwater) based on local water quality criteria. Since its development in the 1960s, it has become a popular tool due to its generalised structure and ease-of-use. Commonly, WQI models involve four consecutive stages; these are (1) selection of the water quality parameters, (2) generation of sub-indices for each parameter (3) calculation of the parameter weighting values, and (4) aggregation of sub-indices to compute the overall water quality index. Several researchers have utilized a range of applications of WQI models to evaluate the water quality of rivers, lakes, reservoirs, and estuaries. Some problems of the WQI model are that they are usually developed based on site-specific guidelines for a particular region, and are therefore not generic. Moreover, they produce uncertainty in the conversion of large amounts of water quality data into a single index.
This paper presents a comparative discussion of the most commonly used WQI models, including the different model structures, components, and applications. Particular focus is placed on parameterization of the models, the techniques used to determine the sub-indices, parameter weighting values, index aggregation functions and the sources of uncertainty. Issues affecting model accuracy are also discussed.