The plain of El-Outaya is located in arid zone of the Saharan Atlas in southern Algeria. The groundwater are characterized by an Important and variability of the salinity. The geology indicates that the plain is constituted by evaporitic rocks. The Dj. El Melah (trias) takes a very important place in the geology of the plain by its lithological composition and its abnormal contacts with the formations around.  Evaporation in the area is very important and consumes the majority of the precipitations.  The heterogeneity of the aquifer of neogene is caused by the presence of clay in variable proportions. The combination between the tools, geological, hydrodynamic, statistical and chemical in the study of the mineralisation allowed us to determine its origin and its evolution in the space.  The analysis of groundwater samples indicates the presence in strong concentrations of Cl-, SO42-, Na+ and Mg2+.