The volcanic nature of the Azores archipelago explains the occurrence of hydromineral resources, with a large range of chemical types and magnitude of mineralization. The mineral water discharges are located in seven of the nine islands of the archipelago, mainly in São Miguel, where the main water types are Na-HCO3 and Na-Cl. The Centre of Volcanology and Geological Hazards Assessment developed a volcanic monitoring system in the Azores, including hydrogeochemical surveillance, that supports the civil protection authorities. In such system, nowadays 12 mineral water discharges are quarterly sampled in São Miguel island, including the measurement of the temperature, pH, electrical conductivity, dissolved CO2, alkalinity, chloride and sulfate. The several parameters depict between years 1992 and 2013 a rather stability trend, with some changes due to mixture with meteoric waters. This trend suggests that the water chemistry can be useful for volcanic surveillance scheme, as is possible to draw the system baseline.