To supply safe and tasty hot water for a long duration by providing a silver-bearing activated carbon having water purifying function and anti-bacterial property with an adsorbing means to which a compound containing a specified number of various types of calcium compounds or magnesium compounds are deposited.

Raw water is heated by installing a heater 3 in a tank 2 having a raw water inlet 1. An adsorbent layer 4 is installed in the rear stage of the tank 2 and immediate before the hot water outlet 7 and also immediate before a filter 6 to filter hot water. The adsorbent layer 4 is filled with silver-bearing activated carbon 5 of which the surface is coated with a compound containing at least one kind of calcium compounds or magnesium compounds. THM, moldy odor, bleaching powder odor, etc., in the raw water can be eliminated and microbe propagation can be suppressed by the silver-bearing activated carbon 5. With this constitution, the effect of silver is retained and safe hot water can be supplied.