H2O, or water, is considered neutral in terms of acidity and basicity. It is neither an acid nor a base. Water molecules can, however, act as both an acid and a base in certain chemical reactions. This property is known as amphotericity. In the presence of a stronger acid, water can act as a base by accepting a proton (H+), and in the presence of a stronger base, it can act as an acid by donating a proton.