Water quality refers to the chemical, physical, biological, and radiological characteristics of water. It is a measure of the condition of water relative to the requirements of one or more biotic species and it is most frequently used by reference to a set of standards against which compliance can be assessed. The most common used to assess water quality relate to health of ecosystems, safety of human contact. In the setting of standards, agencies make political and technical/scientific decisions about how the water will be used, in the case of natural water bodies, they also make some reasonable estimate of pristine conditions. Natural water bodies will vary in response to environmental conditions, Environmental scientists work to understand how these systems function, which in turn helps to identify the sources and fates of contaminants. Environmental lawyers and policymakers work to define legislation with the intention that water is maintained at a quality for its identified use. The vast majority of water on the Earth is neither potable nor toxic. This remains true when seawater in the oceans is not counted, another general perception of water quality is that of a simple property that tells whether water is polluted or not. In fact, water quality is a subject, in part because water is a complex medium intrinsically tied to the ecology of the Earth. Industrial and commercial activities are a cause of water pollution as are runoff from agricultural areas, urban runoff. The parameters for water quality are determined by the intended use, work in the area of water quality tends to be focused on water that is treated for human consumption, industrial use, or in the environment. Water quality depends on the geology and ecosystem, as well as human uses such as sewage dispersion, industrial pollution, use of water bodies as a heat sink. The United States Environmental Protection Agency limits the amounts of contaminants in tap water provided by US public water systems. The U. S. Food and Drug Administration regulations establish limits for contaminants in bottled water that must provide the protection for public health. Drinking water, including bottled water, may reasonably be expected to contain at least small amounts of some contaminants, the presence of these contaminants does not necessarily indicate that the water poses a health risk. Water drawn directly from a stream, lake, or aquifer, dissolved minerals may affect suitability of water for a range of industrial and domestic purposes. Hard water may be softened to remove these ions, the softening process often substitutes sodium cations. Hard water may be preferable to soft water for consumption, since health problems have been associated with excess sodium
Satirical cartoon by William Heath, showing a woman observing monsters in a drop of London water (at the time of the Commission on the London Water Supply report, 1828)
An automated sampling station installed along the East Branch Milwaukee River, New Fane, Wisconsin. The cover of the 24-bottle autosampler (center) is partially raised, showing the sample bottles inside. The autosampler was programmed to collect samples at time intervals, or proportionate to flow over a specified period. The data logger (white cabinet) recorded temperature, specific conductance, and dissolved oxygen levels.
Filtering a manually collected water sample (grab sample) for analysis