A Systematic Review and Meta-Analysis of Water Quality Indices

Water quality indices (WQI) are useful tools for indicating the suitability of water for an expected use. However, they can suffer from some problems. The objective of this paper was to analyze the development of WQI to determine which parameters are used in water quality assessment and to discuss the characteristics of WQI. To screen articles on WQI, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) method is applied to include or exclude articles. Four necessary steps are needed to design WQI: parameter selection, standardization, weighting and aggregation. A set of six methods of aggregations of sub-indices are identified: the arithmetic mean, the geometric mean, the root square, the logarithmic function, the fuzzy inference and the minimum operator. The problems encountered for the overall index are different according to the form of aggregation. They are eclipsing, ambiguity, rigidity or flexibility, adaptability and compensation. The chemical parameters (70%) are the most used in the development of WQI with the physical parameters used at 24% and the biological parameters at 6%. Dissolved oxygen (DO, 87%), total coliforms (87%), biological oxygen demand (BOD, 73%), pH (73%), temperature (67%), turbidity (60%), ammonia (53%), ammonium (47%) and total dissolved solids (47%) are the most commonly used parameters for water quality assessment.