Groundwater quality assessment using entropy weighted water quality index (EWQI) in Lenjanat, Iran

Human health is strongly influenced by water quality which is threatened by the poor quality of polluted groundwater. In this study, the groundwater quality and its suitability for drinking have been studied in Lenjanat plain aquifer, Iran. Fifty-nine groundwater samples from study area were evaluated based on WHO and Iranian standards for drinking water. Groundwater samples from selected monitoring sources were sampled seasonally during 2009-2010. Physical and chemical parameters of groundwater such as electrical conductivity, pH, total dissolved solids, Ca2+, Na+, K+, Mg2+, HCO3-, SO42-, Cl-, F- and NO3- were determined. During the water quality index calculating process, the weight of each parameter is usually given by experts according to their practical experience, which is subjective, so much useful and valuable information about the water quality gets lost. In order to avoid personal judgments about the weight of parameters, an information entropy method was used to assign weight to each parameter. Calculation of entropy weighted water quality index(EWQI) for groundwater samples showed that in the wet season, over 57 and 74 % of samples were in the range of "excellent'' to "medium'' quality based on WHO and Iranian standards, respectively. Due to groundwater quality reduction during dry season, 42 and 62 % of samples were in the range of "excellent'' to "medium'' quality based on WHO and Iranian standards, respectively. The results indicate that application of the EWQI is very useful to help the public and decision-makers will be able to identify and to evaluate groundwater quality in Lenjanat, Iran.