Catalyzes the reversible hydration of carbon dioxide. Can also hydrate cyanamide to urea. Involved in the regulation of fluid secretion into the anterior chamber of the eye. Essential for bone resorption and osteoclast differentiation. Contributes to intracellular pH regulation in the duodenal upper villous epithelium during proton-coupled peptide absorption. Stimulates the chloride-bicarbonate exchange activity of SLC26A6