Because of its semi-arid climate, Morocco constructed a great number of dams in order to satisfy its essential needs. The Sidi Abderrahmane reservoir is part of the catchment area of Oum Rbia River. The setting of the water stopping was carried out in 1965. Its vocation is the drinking water, industries and the irrigation. To study the water quality of the reservoir and evaluate the different relationships between the indicators of faecal pollution (E. coli and FS) and physicochemical parameters in the surface water samples, a total of 36 water samples were collected from 6 stations (upstream, central and downstream) over two periods, January and July 2019 representing respectively rain and dray period. The results of this work showed that physico-chemical water quality parameters of the Sidi Abderrahmane reservoir are within the recommended WHO and Moroccan guideline values for potable water quality, whereas the microbial levels do not meet the standards. These findings were corroborated by the application of the Principal Component Analysis (PCA) and confirmed a seasonality distribution of the physicochemical and microbial parameters between the studied stations. Monitoring and better understanding of the water resources are necessary to anticipate and develop measures to adapt to climate and water use changes.