Water pollution is not strictly defined and fixed standards. Water quality can be required: ① to maintain the natural state; ② meet the requirements of raw drinking water; ③ for fish survival and breeding; ④ suitable for agricultural irrigation; ⑤ suitable for swimming and other water sports activities; ⑥ consistent with a variety of industrial water raw water The requirements; ⑦ does not show the status of dirty. For the water quality of these bodies, many countries have specific requirements. China promulgated the "Surface Water Environmental Quality Standard" as a basis for controlling water pollution. Water pollution sources come mainly from domestic sewage, industrial wastewater, agricultural wastewater and precipitation runoff caused by groundwater; groundwater bodies in the coastal areas, as well as sea water intrusion. Water pollutants are: ① pathogens, such as germs, viruses and parasite eggs; ② from animals and plants of organic matter, such as animal and plant feces, animal and plant debris, the body's components, and their bacteria in the water The role of consumption of dissolved oxygen; ③ plant nutrients, mainly nitrogen and phosphorus compounds, will make the waters of emberiza eutrophication; ④ toxic and hazardous chemicals, such as chlorine pesticides (DDT, BHC, etc.) , Heavy metal salts, radioactive substances, etc .; ⑤ others, such as oil, acid, alkali, warm water, suspended solids, etc. (see wastewater quality). Some of the pollutants entering the water body can be degraded under the action of microorganisms, such as organic matter in domestic sewage, most of which are converted into inorganic substances such as bicarbonate, nitrate and sulfate under the action of bacteria. Some of them can not be degraded, Inorganic pollutants. Degradation of water bodies, dilution and the surrounding environment, such as the role of the exchange of oxygen (from the air in the air to absorb oxygen), making the water quality of con***inated water tends to recover ability, known as self-purification capabilities. When the amount of pollutants does not exceed the self-cleaning capacity, the water body to maintain a normal state; when more than self-purification capacity, the water will show unclean state.

Water pollution control measures, in addition to strengthening the management of pollution sources to reduce the amount of waste water and pollution, the government should develop and promulgate laws and regulations to control the discharge of waste water, such as the Chinese government enacted and promulgated the "******* water pollution Prevention Law "," Industrial "three wastes" emission standards "and other laws and regulations. Town should be the construction of a complete drainage system and wastewater treatment plant, and the development and implementation of management system. Industrial layout and process to consider the environmental requirements. Production wastewater must be treated before leaving the factory (see industrial waste water treatment) and wastewater reuse, especially the establishment of wastewater irrigation system, is an effective way to prevent wastewater from polluting water.