As the influent water for treatment, in addition to the dissolved salt, the surface water or brackish water in the raw water contains mostly large and small visible invisible particles, colloids and other suspended solids, sediments and other impurities, especially surface water. In order to remove these impurities, we can use filter materials containing different media such as quartz sand, gravel, anthracite, etc. as the filter of the filter bed to treat the raw water. The filter has single-layer and multi-layer media filters, which mainly use its mechanical interception function to intercept particles, suspended solids, sediments, etc., to achieve the effect of water purification and pollution interception. As long as the trapped impurities are removed after regular backwashing operation, the media filter can work again.