The invention relates to an empty-solarization-preventing water heater. The empty-solarization-preventing water heater comprises transparent tubes, heat collecting tubes and a water storage tank. The upper end of each heat collecting tube is divided into two branch tubes communicating with each other, wherein the two branch tubes are the flow guide tube and the solarization preventing tube. The flow guide tubes communicate with the water storage tank, and the solarization preventing tubes communicate with a solarization preventing barrel located on the lower portion of the water storage tank. A one-way valve only allowing water to flow out from the solarization preventing barrel is installed in each solarization preventing tube. The top of the solarization preventing barrel communicates with the water storage tank. A piston plate capable of freely sliding along the axis of the solarization preventing barrel is installed in the solarization preventing barrel. The piston plate is connected with the bottom of the solarization preventing barrel through a compression spring. The bottom of the solarization preventing barrel further communicates with a constant pressure water supplementation tube. The water heater can always keep water stored in the heat collecting tubes and effectively protect the heat collecting tubes against empty solarization so as to protect the heat collecting tubes, and the service life of the water heater is prolonged.