The preceding ionization reactions suggest that water may function as both a base (as in its reaction with hydrogen fluoride) and an acid (as in its reaction with ammonia). Species capable of either donating or accepting protons are called amphiprotic, or, more generally, amphoteric, a term used for acids and bases per definitions other than the Brønsted-Lowry one. The equations below show the two possible acid-base reactions for two amphiprotic species, bicarbonate ion, and water:

HCO₃^–_(aq) + H2O _(l)

CO3₂^–_(aq) + H3O⁺ _(aq)

HCO₃^–_(aq) +H2O _(l)

H₂CO_{3 (aq)} + OH^–_(aq)