Isotopic and hydrochemical methods were used to study groundwater mineralization and recharge in the Quaternary aquifer between Erfoud and Rissani in central-eastern Morocco. This area is characterized by an arid to Saharan climate with high average temperatures, low rainfall of less than 80 mm and evapotranspiration values in excess of 1000 mm. It is undergoing a process of desertification in the form of silting-up, plant cover degradation, soils’ salinization, water tables’ depletion and water and wind erosion. Groundwater is stored in the Quaternary aquifer, which is underlain by more or less cemented conglomerates and lacustrine sandstone limestones that contain the essential reserves of the water table. Knowledge of the origin of the water’s chemical degradation, as well as the mechanisms of groundwater recharge, would contribute to sustainable water and soil management in the region. This work involved sampling campaigns, in situ measurements, chemical and isotopic element analyses and the use of advanced investigative methods such as the application of advanced statistical analyses (principal component analysis, preparation of piezometric maps, etc.). The main results show a chemical degradation of the water caused by progressive salinity. The salt manifestation comes from irrigation water. Quaternary water from the Tafilalet plain, shows average values of δ18Omoy = –6.7‰ and δ2Hmoy = –48 ‰, with tritium activity varying in a wide range, between 9 and 20 TU, indicating recent recharge made under current climatic conditions.