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A practical definition of water pollution is: "Water pollution is the addition of substances or energy forms that directly or indirectly alter the nature of the water body in such a manner that negatively affects its legitimate uses." [1]: 6 Water is typically referred to as polluted when it is impaired by anthropogenic contaminants.
Water pollution is the contamination of natural water bodies by chemical, physical, radioactive or pathogenic microbial substances. [2] Point sources of water pollution are described by the CWA as "any discernible, confined, and discrete conveyance from which pollutants are or may be discharged."
Topsoil runoff from farm, central Iowa (2011). Water pollution in the United States is a growing problem that became critical in the 19th century with the development of mechanized agriculture, mining, and manufacturing industries—although laws and regulations introduced in the late 20th century have improved water quality in many water bodies. [1]
Nonpoint source (NPS) pollution refers to diffuse contamination (or pollution) of water or air that does not originate from a single discrete source. This type of pollution is often the cumulative effect of small amounts of contaminants gathered from a large area. It is in contrast to point source pollution which results from a single source.
The definition of NPS water pollution is open to interpretation. However, federal regulation under the CWA provides a specific legal definition for the term. A "nonpoint source" is defined as any source of water pollution that is not a "point source" as defined in CWA section 502(14). [26]
The U.S. Clean Water Act also defines municipal separate storm sewer systems and industrial stormwater discharges (such as construction sites) as point sources. [4] Man-made, natural, and groundwater reservoirs can all be contaminated by point source pollution which can threaten human health and safety. [5] Noise pollution from a jet engine [6] [7]
Water pollution occurs when water bodies, such as rivers, lakes and oceans are contaminated with harmful substances. These substances degrade the water quality and are toxic to humans as consumers and to the environment. [7] The contamination in a river can come from a point source or non-point source pollution. [8]
The CWA definition is excluded for sewage discharged from certain classes of vessels, meaning that a common and important class of water pollution is, by definition, not considered a pollutant for purposes of the United States' primary water quality law. [3] (See Regulation of ship pollution in the United States.)