Energy-saving water heater

The utility model provides an energy-saving water heater and relates to the technical field of heat exchange devices. The energy-saving water heater is used for solving the problem that an existing water heater wastes energy severely. The energy-saving water heater comprises an inner pipe and an outer pipe. The outer pipe comprises an upper sealing cover, a lower sealing cover, and a plurality of cavities communicated with the upper sealing cover and the lower sealing cover. The inner pipe is arranged in an S shape and penetrates through each cavity. The inner pipe is communicated with a heating pipeline. A cavity between the inner pipe and the outer pipe is communicated with a tap water pipeline, and an electric heater and a temperature sensor are arranged in the cavity between the outer pipe and the inner pipe. The electric heater is connected with a control cabinet. The temperature sensor is connected with the control cabinet. The inner pipe is communicated with the heating pipeline, during a heating period, hot water can be obtained without consuming electric energy, under the effect of the electric heater, the hot water at different temperatures is obtained, heat is dissipated into a room through the outer pipe, the indoor temperature can be appropriate, the left hot water can not be cooled automatically, and the hot water can be fully stored so that a user can use the hot water at any time, and energy is saved.