The ultimate purpose of this study is to assess the quality of the water surface of Oued Inaouen and its tributaries and some underground stations before and after the discharge of the city of Taza. It addresses the leachate of the unauthorized landfill of Taza which is a source of nuisance that adds to the many problems of contamination of the surrounding environment if they are not treated before discharge. This survey explains how the landfill can affect the quality of water resources near the city of Taza, represented by the main tributaries of the watershed of Oued Inaouen by determining the main parameters indicators of pollution and studying the possibilities of contamination of groundwater and surface water by infiltration or flow of leachate. Physico-chemical results show high concentrations of organic matter, the BOD5/COD ratio indicating a biodegradable organic fraction. As far as mineral pollution is concerned, high contents of NH4+, NO3-, total phosphorus, and Cl-, which explains the high conductivity values. Bacteriological analyses show significant quantities of coliforms and fecal streptococci. For the evaluation of the pollution of groundwater and surface water, the results obtained are translated by the presence of significant contamination that differs from one point to another. To evaluate the pollution of groundwater and water surface, the results obtained are translated by the presence of significant contamination that differs from one point to another.