Diagnostic of water quality for public supply: study of two withdraws points in the Monjolinho watershed (São Carlos/SP)

Abstract

The water quality of a water body is modified by weather variables such as rainfall and temperature and by domestic and industrial effluents due to the use and occupation of land. With the concern that human activities may influence the water quality providing risks to human health, this study aimed to estimate the Water Quality Index (WQI) and the Toxic Compounds Contamination Index (TCI) to diagnose the condition of water quality for human use. The limnological variables of surface water and underground were analysed in situ and in the laboratory, in two distinct sites in the city of São Carlos/SP during two hydrological periods (drought and flood). The variables corresponding to the WQI were: turbidity, dissolved oxygen, biochemical oxygen demand, pH, electrical conductivity, total nitrogen and total phosphorus concentration and coliforms. For the calculation of the TCI, the variables used were Ni, Fe, Cd, Pb, Cu, Cr, Mn and Zn, total phenolics and cyanide. Based on the results of the WQI (groundwater: 88.9; surface water: 62.3), it was found that groundwater presented the best quality both drought and flood periods. Both groundwater and surface water presented high concentrations of metal ions (Ni: 0.11 mg. L^-1; Cd: 0.09 mg. L^-1; Pb: 0.26 mg. L^-1), indicating the importance of integrating various indexes to obtain more accurate results about the potential use of the water, in order to maintain the quality of both surface water and groundwater for the human use, in accordance with the current legislation.