Calcium hydroxide waters issue from four partly serpentinized Alpine-type ultramafic bodies in the western United States. The occurrence of calcium-hydroxide-type water is restricted to fresh Alpine-type ultramafic rocks. The calcium hydroxide waters are unsaturated with Mg end-member olivine and pyroxene but supersaturated with Mg end-member brucite and serpentine and thus have chemical potentials to cause Serpentinization. The calcium hydroxide waters are isotopically similar to the common magnesium bicarbonate meteoric waters peculiar to ultramafic rocks and serpentinites. Some Serpentinization is apparently a near-surface phenomenon occurring at present. The Serpentinization takes place at nearly constant composition, except for loss of CaO.