Adapting the National Sanitation Foundation water quality index to the Brazilian semiarid

Knowledge of the water quality of a reservoir used for human consumption is important. Water quality indices are used to facilitate understanding of this quality. This study aimed to adapt and compare the water quality index of the National Sanitation Foundation to the physical, chemical and biological conditions of artificial reservoirs in regions with tropical semiarid climate and its spatio-temporal variability. Twelve water samples were taken between April 2008 to April 2010 in seven sampling points distributed in Oros reservoir in the southern of Ceara. Water quality attributes that were monitored and used for calculation and adjustment of the index were: pH, temperature, dissolved oxygen, biochemical oxygen demand, total phosphorus, nitrate, total solids, turbidity and fecal coliform. From them, we used the Principal Component Analysis to determine the weights to be associated with the parameters of the water quality index and adapt it to reservoirs of semiarid climates. The water quality of the reservoir was classified as regular for most of the study period. Although varying with rainfall, there was effect of seasonality on water quality. It was observed that the index adapted to semiarid climate regions is statistically different from indices from other regions. However, the difference is observed only in sensitivity and weigths of determining attributes quality.