Abstract
Since Horton in 1965, many authors have sought to aggregate different variables characterizing the state of water into a single value called Water Quality Index ( W Q I ). This index is intended to facilitate the operational management of water resources and their allocation for different uses. Detailed and operational description of the main W Q I calculations are here reviewed. The review contains: (1) an historical analysis of the evolution of W Q I calculation methods by looking both at the choice of variables, the methods of weighting and aggregating these variables into a final single value; (2) an illustration of the contradictions observed in the final result when, on the same database, the W Q I is calculated by different methods; (3) the significant progress possible via fuzzy logic to define a W Q I adapted to specific water use.
Highlights
The increasing population, the expansion of economic activities, and urban sprawl are leading to increased demand for water
The logarithmic and arithmetic index proposed by Tiwari and Mishra (TMWQI) [47], the arithmetic index proposed by Ramakrishnaiah et al (RWQI) [62], the harmonic square average index proposed by Council of Ministers of the Environment (CCME) (CCMEWQI) [64] and the fuzzy logic Water Quality Index (WQI) proposed by icaga (FWQI) [52] were compared using the same dataset
The subindex used in the aggregation decreases exponentially, which leads to a downgrade of the water quality into “unsuitable” class
Summary
The increasing population, the expansion of economic activities, and urban sprawl are leading to increased demand for water. In Europe, Prati et al 1971 [12] proposed another index based upon water quality standards (see Appendix A.3 for calculation details) Their idea consists of transforming concentrations of pollutants into levels of pollution. Dinius 1972 [32] proposed another WQI, based upon Horton’s index, in order to calculate the costs of remediation of water pollution in Alabama (USA) This WQI defines a decreasing scale from 100 to 0, where the value 100 is assigned to the “perfect” quality water (see Appendix A.4 for calculation details). In India, Bhargava 1983 [14]’s studies introduced a new WQI where the combination of variables highlights the pollution load He defined later the variables to be introduced and specified the WQI’s formula according to the water use [46] (see Appendix B.2 for calculation details). Disagreements appear in three cases: (i) the same WQI is used, but the limits of classes differ; (ii) different WQIs are used, on the basis of the same variables, and lead to different classifications; (iii) different WQIs are used, on the basis of different types or numbers of variables
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