A high-efficiency water boiler includes a shell and a heating unit located in the shell. The heating unit includes a heating tank filled with fuel and a heater for heating the fuel. A containing unit includes a container provided around the heating tank. A heat conduction unit includes heat conduction pipes leading to the container from the heating tank to transfer heat to the container from the heating tank. A cooling unit includes a heat exchanger for cooling the fuel going therein from the heating tank. An inlet pipe extends through the heat exchanger and includes an end connected to a leading section of the container so that water can go into the container through the inlet pipe. An outlet pipe is connected to a tailing section of the container so that the water can leave the container through the outlet pipe.