Water quality laws govern the protection of water resources for human health and the environment. Water quality laws are legal standards or requirements governing water quality, that is, the concentrations of water pollutants in some regulated volume of water. Such standards are generally expressed as levels of a specific water pollutants (whether chemical, physical, biological, or radiological) that are deemed acceptable in the water volume, and are generally designed relative to the water's intended use - whether for human consumption, industrial or domestic use, recreation, or as aquatic habitat. Additionally, these laws provide regulations on the alteration of the chemical, physical, radiological, and biological characteristics of water resources. Regulatory efforts may include identifying and categorizing water pollutants, dictating acceptable pollutant concentrations in water resources, and limiting pollutant discharges from effluent sources. Regulatory areas include sewage treatment and disposal, industrial and agricultural waste water management, and control of surface runoff from construction sites and urban environments. Water quality laws provides the foundation for regulations in water standards, monitoring, required inspections and permits, and enforcement. These laws may be modified to meet current needs and priorities.
Regulated waters The Earth's hydrosphere is ubiquitous, fluid, and complex. Within the water cycle, physical water moves without regard to political boundaries between the Earth's atmosphere, surface, and subsurface, through both natural and human-made channels.
Regulated waters Water quality laws define the portion of this complex system subject to regulatory control. Regulatory jurisdictions may be coterminous with political boundaries (e.g., certain treaty responsibilities may apply to water pollution in all of Earth's international waters). Other laws may apply only to a subset of waters within a political boundary (e.g., a national law that applies only to navigable surface waters), or to a special class of water (e.g., drinking water resources).
Non-regulated waters Areas not covered by regulated waters. Additionally, cross-jurisdictional waters may be subject to cross-jurisdictional agreements. Even within jurisdictions, complexities may arise where water flows between subsurface and surface, or saturates land without permanently inundating it (wetlands).
Water pollutant classification Water quality laws identify the substances and energies which qualify as "water pollution" for purposes of further control. From a regulatory perspective, this requires defining the class(es) of materials that qualify as pollutants, and the activities that transform a material into a pollutant. Regulatory administrations may also use definitions to reflect policy decisions, excluding certain classes of materials from the definition of water pollution that would otherwise be considered to constitute water pollution. For example, the United States Clean Water Act (CWA) defines "pollution" (i.e., water pollution) very broadly to include any and all "man-made or man-induced alteration of the chemical, physical, biological, and radiological integrity of water." However, the Act defines "pollutants" subject to its control more specifically, as "dredged spoil, solid waste, incinerator residue, filter backwash, sewage, garbage, sewage sludge, munitions, chemical wastes, biological materials, radioactive materials [with certain exceptions], heat, wrecked or discarded equipment, rock, sand, cellar dirt and industrial, municipal, and agricultural waste discharged into water." This definition begins to define both the classes or types of materials (e.g., solid waste) and energies (e.g., heat) that may constitute water pollution, and indicates the moment at which otherwise useful materials may be transformed into pollution for regulatory purposes: when they are "discharged into water," defined elsewhere as "addition" of the material to regulated waters. 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. (See Regulation of ship pollution in the United States.) Although thermal pollution is subject to regulation under the CWA, definitional questions have resulted in litigation, including whether even water itself may qualify as a "pollutant" (e.g., adding warm water to a stream). The United States Supreme Court addressed these issues in Los Angeles County Flood Control District v. Natural Resources Defense Council, Inc. (2013).
Water quality standards
Ambient water quality standards Determining appropriate water quality standards generally requires up-to-date scientific data on the health or environmental effects of the pollutant under review through water quality criteria. Water quality criteria includes set indicators that determine if water is no longer safe for human health or wildlife based on scientific data. Scientific data includes measurable factors such as temperature, dissolved oxygen, nutrients, toxic chemicals, pollutants, heavy metals, organic micro pollutants, radioactive substances, and sediments. Water quality criteria may require periodic or continuous monitoring of the water body. Based on the criteria, regulatory decisions on water quality standards may change to also incorporate political considerations, such as the economic costs and benefits of compliance. As an example, the United States employs water quality standards as part of its regulation of surface water quality under the CWA. The national Water Quality Standards (WQS) Program begins with U.S. states designating intended uses (e.g., recreation, drinking water, natural habitat) for a surface water bodies, after which they develop science-based water quality criteria. The criteria include numeric pollutant concentration limits, narrative goals (e.g., free from algae blooms), and narrative biological criteria (i.e., the aquatic life that should be able to live in the waterbody). If the water body fails the existing WQS criteria, the state develops a Total Maximum Daily Load (TMDL) for pollutants of concern. Human activity impacting water quality will then be controlled via other regulatory means in order to achieve the TMDL targets.
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