Development of a Water Quality Index (WQI) for public supply in the Vale do Rio Pardo region, RS, Brazil

Abstract

This research developed a Water Quality Index (WQI) for public supply in the Vale do Rio Pardo Region, RS, Brazil (WQI-VRP), from the database of the 13th Regional Health Coordination, totaling 1175 samples. A filtration process resulted in 285 samples with the variables free residual chlorine, turbidity, apparent color, pH, fluoride, total coliforms and Escherichia coli. For water consumption purposes, the Water Quality Index developed by the Sanitation Company of Goiás, Brazil, was used. A multivariate calibration of the weights of importance of the parameters included in the original index was performed, resulting in the WQI-VRP. Comparing the medians of the two indexes, it was found that there were significant differences (p<0.05), qualifying the WQI-VRP as more restrictive. The results indicated that 89.8% of the samples were classified as non-compliant samples by WQI-VRP, while 10.2% were classified as compliant samples. Of the 285 samples analyzed, 72 samples of chlorine, 12 of total coliform, 5 of E. coli, 2 of color, 200 of fluoride and 26 of pH, were below or above the minimum or maximum values required by Brazilian legislation. The pH and fluoride correspond to the critical variables of the study region, as they were the parameters that showed the greatest increases in relative weights when comparing the original index with the calibrated one. These results confirm the use of the WQI-VRP as an efficient tool to assess the quality of drinking water in Brazilian subtropical and temperate lotic systems.