The isotopic composition of the waters sampled in the Hydrogeological Unit Yunquera-Nieves are from Mediterranean and Atlantic origin. The lsO and 2H contents define a local meteoric water line with lower slope than mundial meteoric water line, because of the evaporation process. The mineralization and isotopic composition of the waters decreases with the altitude, which allow us delimite the recharge surface of the main springs of the Unit. The mineralization and the isotopic composition of rainwater vary inversely to the amount of precipitation. The springwaters deplete their mineralization and isotopic content in response to the outflow increase because of the important winter precipitations. Anyway, the responses are quick, which probe the karstic behaviour of the springs