A dataset on the chemical composition of mineral water discharges from São Miguel, 76 samples, depicts a large variability of
chemical types and dissolved solids content. The distribution of the discharges shows an association with the three active Quaternary
central volcanoes that dominate the geology of São Miguel, namely Furnas, Fogo and Sete Cidades, 74% of which are springs, 13%
fumaroles, 12% wells and 1% hand-dug wells. Total dissolved solids (TDS) values are in the range of 159–20 957 mg l-1
, discharge
temperature varies from 15 to 99.58C and waters are mainly strongly acid to slightly alkaline (pH ranging between 2.2 and 7.71).
Springs discharge mainly from perched-water bodies, corresponding to Na-HCO3 and Na-HCO3-Cl-type waters, with a composition
influenced by absorption of CO2 and mixing between meteoric water and boiling waters with a hydrothermal component. Instead the
majority of the wells are distributed along the coast and depict chloride enrichment owing to mixture with seawater. The lower pH
values are associated with boiling pools at Fogo Volcano with a SO4-dominated chemistry, resulting from steam-heating of shallow
perched-water bodies.