Mineral waters were monthly sampled in selected springs from Furnas and Fogo trachytic central volcanoes (São Miguel, Azores, Portugal).Water temperatures between 15.1 °C and 90.2°C, characterize poorly mineralized waters ofNa–HCO3 and Na–HCO3–Cl types. According to the spring location, two watersheds were selected in each volcano to evaluate solute fluxes and chemical weathering rates (Fogo volcano: Ribeira Grande river — RRG; Furnas volcano: Ribeira Quente river — RRQ). Na, Mg, K and Ca fluxes in groundwater represented 43%, 60%, 46% and 57% ofthe total (subsurface plus surface fluxes) in RRG, and respectively 43%, 53%, 46% and 49% in RRQ. Average HCO3 flux is ten times higher in RRQ (130.1 × 106 mol/yr) compared to RRG (13.8 × 106 mol/yr), reflecting the volcano degassing and the lower ratio between groundwater and river water fluxes. Based on these values, total CO2-consumption by weathering ranged from 1.5 × 106 mol/km2/yr (RRG) to 4 × 106 mol/km2/yr (RRQ). TDS load varied between 3772 t/yr (RRG) and 15388 t/yr (RRQ), and the ratio between values ingroundwater and in surface water is respectively equal to 0.72 and 2.04. The associated chemical weathering rates in groundwater were 206 t/km2/yr (RRG) and399 t/km2/yr (RRQ). Coupled to river water, these values indicate that total chemical weathering rates are respectively equal to 493 t/km2/yr and 594 t/km2/yr. A similar approach developed for the entire archipelago showed that the chemical weathering rates due to groundwater are in the range from 33 to 321 t/km2/yr, being partially controlled by the age of the islands. Results of the present study point out to the need to consider groundwater solute fluxes due to weathering when establishing geochemical budgets.