Water pollution index – A new integrated approach to rank water quality

Abstract

Several indices have been developed to define water quality for human consumption, but each one has some drawbacks that limit their wide applicability. So there is a need for a new approach to classify water quality that can be accepted universally. Pollution load or water quality status of Birbhum district of West Bengal, India was presented by applying newly formulated water pollution index (WPI) method in 368 groundwater samples (184 in each pre and post monsoon season). This new technique is flexible and easy to calculate compared to the existing methods. According to this new approach water quality is principally based on observed concentration (Ci) and standard permissible concentration (Si); and can be adjusted to the number of total applied variables (n) as user wants. WPI suggested four categories of water quality: WPI < 0.5 signifies an excellent quality, 0.5 > WPI < 0.75 indicates good quality, 0.75 > WPI < 1 is moderately polluted water, whereas if WPI > 1, indicates highly polluted water. In this study area, WPI ranged from 0.38 to 1.94 with a mean value of 0.831, indicating groundwater quality as moderately polluted. As per WPI results, 12% 55%, 16%, 17% samples in PRM and 2%, 34%, 38%, 26% samples in POM were found as excellent, good, moderately polluted and highly polluted water respectively. Empirical bayesian kriging (EBK) interpolation based GIS spatial map clearly reflected the change in seasonal variation of WPI. Normality test of the data sets were checked through Kolmogorov–Smirnov test and significant difference (p < 0.003) was observed. The new WPI was validated through Bland-Altman analysis using limits of agreement (LoA) and bias value (δ). WPI fitted very well indicating its better applicability and output in diverse water pollution studies than the existing water quality indices.