In short, it is the purification of water. Water purification is a process of removing rust, silt, residual chlorine, organic matter, harmful heavy metal ions, bacteria, viruses, etc. from the water in a physical or chemical manner according to different final water needs through corresponding filter materials. Obviously, if the physical filtration method is used throughout the water purification process, no new substances will be produced or added to the water, and the properties of the water will not be changed. Therefore, it is the safest method and is widely used in Western countries. The water is purified and the substances harmful to human health are removed. We call it "purified water".