The current situation of water resources and their uses in the Sisseb El Alem Nadhour Saouaf basin (Central Tunisia) is under strong pressure; human activities and climate change. To arrive at a realistic assessment of the underground water reserves in this basin, a diversified hydrogeological database was created (data from hydraulic and oil drilling, seismic sections, electrical surveys and gravimetric). A structural model is built and validated for the study area. Such a geomodel results from a geological interpretation, which makes it possible to identify the sedimentary series present and to specify their spatial and chronological relationships. This 3D geological model was integrated to Modflow model to assess the flow dynamic and to calculate the water budget. Many simulations were performed. The balance budget over 2020 will be in deficit -14.22 Mm3 and the aquifer will remain in a critical situation: the exploitation will be of the order of 75.43 Mm3. This depends enormously on the progress of the method of extraction of groundwater and over 2030: the global water budget is also deficit -14.5 Mm3.