<p>A water heater includes: heating means 55 for heating water sent from a lower portion of the hot water tank 57; a circulation pump 63 which sends the water of the lower portion of the hot water tank 57; an outgoing-hot water pipe passage 65 for guiding heated water to an upper portion of the hot water tank 57; and scale suppressing means 68 adding scale suppressing agent 67 to water sent to the heating means 55; and when a temperature of water which flows into the heating means 55 is lower, a concentration of the scale suppressing agent 67 included in water is made greater. Since solubility of the scale suppressing agent 67 with respect to water can be adjusted depending upon operating conditions of the water heater, it is possible to efficiently suppress generation of scale without wasting the scale suppressing agent 67.</p>
