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 man-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