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In El Kef region, Northwestern Tunisia, the evolution of the agricultural and industrial sectors has exacerbated the need for water which caused a significant increase in groundwater extraction. In this context, several geologic and geophysical studies conducted on the groundwater resources of the concerning area were meant to give us insight into the geometry of the reservoirs and structural architecture of the basin and to identify the various reservoirs such as the Mio-Plio-Quaternary, the Lower Eocene and the Campanian–Maastrichtian aquifers. In this study, we used the geochemical study and analysis of gravity data (Horizontal and vertical derivative, horizontal gravity gradient maxima...) to improve the knowledge of the dip and direction fault and the geological structures in El Kef region (NW Tunisia) that control the groundwater hydrodynamic. Furthermore, the techniques of horizontal gradient and upward extension were applied to determine the gravity lineaments that represent the location of density contrasts and to locate the various faults that contribute to the structuring of the study area. Additionally, this study aims to assess the spatio-temporal evolution of the hydrodynamic parameters of the aquifers and to characterize the groundwater mineralization (salinity, chemical facies relationship, etc.). Our study showed the presence of four types of water facies: Ca–Mg–SO4; Na–Cl–NO3; Ca–Mg–HCO3 and Na–K–HCO3. The isotopic study is used to provide some information about the groundwater recharge and to define the different sources of water mixing. That way we could have better understanding to the hydrologic cycle and to the paleoclimate of the study area. Generally, the geochemically evolved groundwaters of the aquifer systems of El Kef region are relatively isotopically depleted when compared to the present day meteoric waters reflecting recharge under cold climate and high altitude. Conversely, the continuous increase of the annual mean temperature and the decrease of precipitations have been observed for the second half of the 20th century in North Africa. It is likely related to the warmer and drier conditions associated with the climate change phenomenon. [ABSTRACT FROM AUTHOR]