The object of this study is the identification of the mechanism that causes the salinization of the groundwaters in two zones in the valley of La Aldea. The stratigraphyc, geochemical and mineralogical studies of a rock series, jointly with a detailed hydrogeological study of the aquiferous system of La Aldea, have permitted to characterize and to identify the salinization of the waters as geological type, due to the presence of some deposits of hydrotermal alterations locally named “azulejos”. Also, this study brings forth the existence of another contamination process in the aquifer due to influences of agricultural doings.