The Andarax river is characterized by the variability of its flow, which is dependent upon the rainfall regime of the area. This work presents a study of the chemical composition of the surface waters of the Andarax river over an annual cycle. It analyses the relationship between ground water and surface waters using a hydrogeochemical methodology. The ground water-surface water interactions was found to be more intense in two areas: the north of Almócita and north of Santa Fe. North of Almócita local discharges of good quality water arise, which leads to the chemical stabilization of the surface water. In this stretch, electrical conductivity, temperature and ion concentrations are constant, and lower than at adjacent sampling points. At north of Santa Fe, in the mid-section of the river, a contrasting effect is observed with an increase in salinity and seasonal variability. Concentrations of Cl- and SO4 2- become elevated, and there is a marked increase in salinity – especially during low flow periods when the majority of the surface flow derives from groundwater drainage