Fluoride content in drinking water supply in São Miguel volcanic island (Azores, Portugal)

► High fluoride content in volcanic rock aquifers is exploited for public water supply. ► Groundwater composition is modified by water-rock interaction and marine airborne salts. ► Fluoride enrichment in perched aquifers is mainly due to silicate weathering. ► High F contents are observed in mineral discharges with a volcanic source.