A method for making a calcium hydroxide solution includes adding water and calcium oxide into a slaking reactor equipped with a stirring means at an upper end and two or more outlets positioned at different heights. The materials are stirred so that a vertical concentration gradient of calcium ions develops within the reactor, producing a clear liquid layer at an upper region and a milk of lime suspension at a lower region. A desired calcium hydroxide solution is obtained by selecting an outlet corresponding to the required concentration of calcium ions.