​A set of 46 springs located in the north flank of Fogo volcano (São Miguel, Azores) were sampled to characterize groundwater chemistry. The majority of the discharge from volcanic rocks with acidic character (95 %), at an elevation range of 200-400 m a.s.l., and the average discharge are usually not higher than 2 L/s. Nevertheless, the discharge in a few springs from trachytic lava flows can be higher (21.3 L/s). A group of 12 surface water samples were also collected twice along the Ribeira Grande River. Groundwater average temperature ranges between 19.6 and 20.7 °C, and it is possible to depict two groups of discharges: thermal waters (16.7 %), with a temperature range from 27.8 to 71.2 °C, and cold waters, with temperature under 20 °C. In this latter group, temperature is inversely proportional to elevation. The average pH and conductivity range, respectively, between 5.7 and 7.8 and 291-425 μS/cm. Nevertheless, higher conductivity values were measured in boiling pools. Groundwater mainly belongs to the Na-HCO₃ to Na-Cl types. The major-ion relative composition of the cold springs shows a decreasing order for cations as Na > Ca > K > Mg and for anions HCO₃ > Cl > SO₄. In thermal discharges the relative composition is, respectively, Na > Ca > K > Mg and SO₄ > HCO₃ > Cl. The average nitrate content ranges from 2.09 to 2.57 mg/L comparing all the sampling periods, and the cumulative probability plot shows that about 75 % of the samples present values lower than 1.98 mg/L. Results show clearly that the higher nitrate measurements are observed in river waters and springs sampled in areas where pasture lands are dominant.