Monitoring water quality is essential to understand the situation of water resources, especially in regions suffering from water scarcity, such as the Brazilian Northeast. The present study aimed to analyze the water quality of the Nilo Coelho reservoir, Terra Nova, using the Water Quality Index proposed by CETESB. Data provided by the HidroWeb portal of the National Water and Basic Sanitation Agency were used. The reservoir has monitoring data for the years 2016 to 2022, still in the present study, the collections from 2019 to 2022 were used because they had the necessary parameters for calculating the index. The parameters used were thermotolerant coliforms, biochemical oxygen demand, total phosphorus, pH, total dissolved solids, temperature, turbidity, dissolved oxygen and nitrate. The results were compared with the limits established by CONAMA No. 357/2005. Among the parameters analyzed, only thermotolerant coliforms, total phosphorus and BOD were outside the limits set by the legislation, which may indicate outbreaks of pollution in the reservoir. The application of the IQA indicates that the water in the reservoir can be classified as good, showing that the water is suitable for human supply. However, continuous monitoring of the region's water is of paramount importance, in addition to the adoption of public policies that encourage the proper management of the areas surrounding the reservoir, since it is receiving water from the São Francisco River transposition project.