Investigating the efficiency of information entropy and fuzzy theories to classification of groundwater samples for drinking purposes: Lenjanat Plain, Central Iran

In this study, the drinking groundwater quality of Lenjanat plain, Iran, is classified based on water quality index (WQI), Takagi–Sugeno–Kang fuzzy water quality index (TSKFWQI) and entropy weighted water quality index (EWQI). Groundwater samples from 79 regional monitoring wells and different resources such as agricultural and potable deep wells, rural dug wells, industrial and recreational facilities and drilled wells in the vicinity of pollution sources of urban and rural sewage discharge points were collected and analyzed during 2009–2010. In this research, physicochemical parameters including As, Pb, Cr, Ni, Cu, NO₃, Na, K, F, Cl, Ba, Ca, Mg, Fe, SO₄ and TDS were used to calculate the drinking quality rank of water samples using WQI, TSKFWQI and EWQI methods. Calculations showed that ranking the groundwater samples using WQI is very similar to ranks determined by entropy-based calculations of water quality index, while the TSKFWQI clearly indicates that this classification method acts stricter than two other methods (WQI and EWQI). In TSKFWQI, the final rank of any sample is very much affected by toxic parameters. It means that a sample with acceptable range of all parameters, except one toxic parameter, falls in the unacceptable rank. As a result, in areas where water chemistry shows the presence of some toxic elements in the groundwater resources, TSKFWQI classification of water with regard to drinking purposes gives more reliable results.