1. Ultrafiltration System (UF): the filtration accuracy is 0.001-0.1 ? m, which belongs to one of the high and new technologies in 21th century. It is a membrane separation technology using pressure difference. Iron rust, sediment, suspended materials, colloid, bacteria, macro-molecular organic matter and other harmful substances in water can be filtered out, and some mineral elements which are beneficial to human body can be retained. It is the core component in the production process of mineral water and mountain spring water. The recovery rate of water in ultra-filtration process is as high as 95%, and it is easy to realize washing and back-washing, which is not easy to block. The service life is relatively long. Ultra-filtration does not need to be charged and pressurized. It can be filtered only by tap water pressure, with large flow rate and low cost. Therefore, the purification of drinking water in the future will be based on ultra-filtration technology, combined with other filtering materials, in order to achieve a wide range of treatment and more comprehensive elimination of pollutants in water.

2. Nanofiltration: filtration accuracy is between ultra-filtration and reverse osmosis, desalinization rate is lower than reverse osmosis. It is also a membrane separation technology which needs to be charged and pressurized. The recovery rate of water is low. That is to say, in the process of making water with nanofiltration membrane, nearly 30% of tap water will be wasted. This is unacceptable to the general household. It is generally used in industrial pure water manufacture.

3. Reverse Osmosis (RO): filtration accuracy is about 0.0001 ? m. In early 60s, the United States developed an ultra-high precision membrane separation technology using differential pressure. It can filter almost all impurities (including harmful and beneficial) in water. Water molecules can only be allowed through. That is to say, in the process of making water with reverse osmosis membrane, nearly 50% tap water will be wasted. This is unacceptable to the general family. It is generally used for pure water, industrial ultra pure water, and pharmaceutical ultra pure water. The technology of reverse osmosis needs to be pressurized, electrified, the flow rate is small, the utilization ratio of water is low, so it is not suitable for the purification of a large number of drinking water.
4. Micro-filtration (MFN): filtration accuracy is generally 0.1-50 microns. Common PP filter, activated carbon filter, ceramic filter, and so on belong to the category of micro-filtration. It is used for simple coarse filtration, filtration of sediment, rust and other large particles impurity in water, but can not remove harmful substances such as bacteria in water. The filter core is usually can not cleaned and is disposable filtration materials , frequent replacement is required. (1) PP cotton core: generally used only for low requirements of coarse filtration, removal of sediment in water, rust and other large particles .(2) active carbon : can eliminate the water color and odour. But the bacteria in the water can not be removed, and the removal of sediment and rust is also very poor. (3) ceramic filter core: the minimum filtration precision is only 0.1 micron, the flow rate is usually small, and it is not easy to clean.