Place high-temperature alumina in a columnar device. When water passes through the high-temperature alumina filled in the columnar container, pollutants and other substances in the water are adsorbed on the surface of the particles. Initially, the upstream of the column becomes saturated, and as more water flows through, the saturation zone moves downward, ultimately reaching full saturation. The defluorination ability of high-temperature alumina is closely related to the pH value of the raw water. When the pH value is 5.5, the adsorption capacity is maximum. Therefore, adjusting the pH value of the raw water to around 5.5 can increase the adsorption efficiency of high-temperature alumina.