The Lobo River reservoir, the main source of drinking water supply for the municipality of Daloa, is facing a deterioration in its quality. This study aims to assess the quality of this resource. The physico-chemical and chemical parameters of this water were determined during the two seasons of the year 2020. The methodological approach consisted firstly of characterizing the water in the reservoir in relation to the WHO guide values; secondly, determining the phenomena that govern the mineralization of this water and, thirdly, calculating the organic pollution index (OPI) and the water quality index (WQI) of the reservoir. The results show that the physico-chemical parameters (T, pH and EC) comply with the WHO guide values. However, the water has a high turbidity, with a very strong colour in all seasons. Phosphate (0.93 mg/L), ammonium (1.48 mg/L), total iron (2.99 mg/L) and manganese (0.66 mg/L) concentrations are high. On the other hand, chlorides, nitrates and nitrites remain low in both seasons. On the other hand, chlorides, nitrates and nitrites remain low in both seasons. Normalized Principal Component Analysis (NPCA) revealed that the mineralization of this water is of natural and anthropogenic origin. The water quality (2.25 to 3.25) and organic pollution (429.73 to 693.31) indices show that the water in the reservoir is unfit for consumption, with moderate pollution in the dry season and heavy pollution in the rainy season.