The groundwater resources of the aquifer of the Aracena mountain range (Huelva) are being studied in
detail by the Spanish Geological Survey. In these studies the hydrochemistry plays a pivotal role and
contributes to validate the hypotheses of hydrogeological functioning based on hydrodynamic data. Several
sampling campaigns have been made to characterize the groundwater from a hydrochemical point of
view and, later, to define the processes of hydrochemical modification that takes place in the direction of
the groundwater flow. In this work the spatial distribution of the main water-types is analyzed and a
synthesis of the groundwater functioning of the Aracena aquifer is made. The foremost presence of calcium
and calcium - magnesium bicarbonate water-types, the low partial pressures of CO2 and the sub-saturation
of the water with respect to calcite and dolomite minerals are the most remarkable features of the
hydrochemistry of the Aracena aquifer