Reverse osmosis is a concept corresponding to osmosis. Gu Ming thought that the solvent (water) in the concentrated solution is pressed into the dilute solution on the other side of the semi-permeable membrane by adding a higher pressure on one side of the concentrated solution than the natural osmotic pressure. This process is contrary to the natural normal osmotic process. Therefore, it can intercept impurities in the water on one side of the membrane, and let the other side of the channel membrane, so as to produce pure water and high-purity water. There are two keys to the production of pure water in reverse osmosis facilities. One is a selective membrane, which we call semi-permeable membrane, but a certain pressure. In short, there are many small pores on the reverse osmosis membrane. The size of these pores is the same as that of water molecules. However, bacteria, viruses, most organic pollutants, and water and ions are much larger than water molecules. Therefore, they cannot be separated from water through the semi-permeable membrane (RO membrane).