This invention relates to a kind of water heater water discharging device and the water heater using this device. The water-discharging device includes the floater, which is set in the heat preserved water storage tank. The upside of floater has the end opening exposed air discharging pipe, which is always keeping above the water surface in the heat preserved water storage tank. The downside of floater has the opening exposed hot water pipe, which is always keeping below the water surface in the heat preserved water storage tank; the other end opening of air discharging pipe and hot water pipe are connected with the air discharging valve port of three-way control valve and the water feeding valve port respectively. The other water discharging valve port of the three-way control valve connects to one end of the water-discharging pipe. The other end of water discharging pipe, the water discharging valve and water feeding valve are connected in parallel; the three-way control valve is controlled and switched by controlling mechanism.