Water pollution

# Overview
Water pollution is a large set of adverse effects upon water bodies such as lakes, rivers, oceans, and groundwater caused by human activities.
Although natural phenomena such as volcanoes, algae blooms, storms, and earthquakes also cause major changes in water quality and the ecological status of water, these are not deemed to be pollution. Water is only called polluted when it is not able to be used for what one wants it to be used for. Water pollution has many causes and characteristics. Increases in nutrient loading may lead to eutrophication. Organic wastes such as sewage impose high oxygen demands on the receiving water leading to oxygen depletion with potentially severe impacts on the whole eco-system. Industries discharge a variety of pollutants in their wastewater including heavy metals, resin pellets, organic toxins, oils, nutrients, and solids. Discharges can also have thermal effects, especially those from power stations, and these too reduce the available oxygen. Silt-bearing runoff from many activities including construction sites, deforestation and agriculture can inhibit the penetration of sunlight through the water column, restricting photosynthesis and causing blanketing of the lake or river bed, in turn damaging ecological systems.
Pollutants in water include a wide spectrum of chemicals, pathogens, and physical chemistry or sensory changes.  Many of the chemical substances are toxic.  Pathogens can produce waterborne diseases in either human or animal hosts. Alteration of water's physical chemistry include acidity, electrical conductivity, temperature, and eutrophication. Eutrophication is the fertilisation of surface water by nutrients that were previously scarce. Even many of the municipal water supplies in developed countries can present health risks. Water pollution is a major problem in the global context. It has been suggested that it is the leading worldwide cause of deaths and diseases, and that it accounts for the deaths of more than 14,000 people daily.

# Sources of water pollution
Some of the principal sources of water pollution are:
- Geology of aquifers from which groundwater is abstracted
- Industrial discharge of chemical wastes and byproducts
- Discharge of poorly-treated or untreated sewage
- Surface runoff containing pesticides or fertilizers
- Slash and burn farming practice, which is often an element within shifting cultivation agricultural systems
- Surface runoff containing spilled petroleum products
- Surface runoff from construction sites, farms, or paved and other impervious surfaces e.g. silt
- Discharge of contaminated and/or heated water used for industrial processes
- Acid rain caused by industrial discharge of sulphur dioxide (by burning high-sulphur fossil fuels)
- Excess nutrients are added (eutrophication) by runoff containing detergents or fertilizers
- Underground storage tank leakage, leading to soil contamination, and hence aquifer contamination
- Inappropriate disposal of various solid wastes and, on a localized scale, littering
- Oil spills

# Contaminants
Contaminants may include organic and inorganic substances.
Some organic water pollutants are:
- Insecticides and herbicides, a huge range of organohalide and other chemicals
- Bacteria, often is from sewage or livestock operations
- Food processing waste, including pathogens
- Tree and brush debris from logging operations
- VOCs (Volatile organic compounds), such as industrial solvents, from improper storage
- Petroleum Hydrocarbons including fuels (gasoline, diesel, jet fuels, and fuel oils)  and lubricants (motor oil) from oil field operations, refineries, pipelines, retail service station's underground storage tanks, and transfer operations.  Note: VOCs include gasoline-range hydrocarbons.
Some inorganic water pollutants include:
- Heavy metals including acid mine drainage
- Acidity caused by industrial discharges (especially sulfur dioxide from power plants)
- Pre-production industrial raw resin pellets, an industrial pollutant
- Chemical waste as industrial by products
- Fertilizers, in runoff from agriculture including nitrates and phosphates
- Silt in surface runoff from construction sites, logging, slash and burn practices or land clearing sites

# Transport and chemical reactions of water pollutants
Most water pollutants are eventually carried by the rivers into the oceans. In some areas of the world the influence can be traced hundred miles from the mouth by studies using hydrology transport models. Advanced computer models such as SWMM or the DSSAM Model have been used in many locations worldwide to examine the fate of pollutants in aquatic systems.  Indicator filter feeding species such as copepods have also been used to study pollutant fates in the New York Bight, for example.  The highest toxin loads are not directly at the mouth of the Hudson River, but 100 kilometers south, since several days are required for incorporation into planktonic tissue. The Hudson discharge flows south along the coast due to coriolis force. Further south then are areas of oxygen depletion, caused by chemicals using up oxygen and by algae blooms, caused by excess nutrients from algal cell death and decomposition.  Fish and shellfish kills have been reported, because toxins climb the foodchain after small fish consume copepods, then large fish eat smaller fish, etc. Each successive step up the food chain causes a stepwise concentration of pollutants such as heavy metals (e.g. mercury) and persistent organic pollutants such as DDT.  This is known as biomagnification which is occasionally used interchangeably with bioaccumulation.
The big gyres in the oceans trap floating plastic debris. The North Pacific Gyre for example has collected the so-called Great Pacific Garbage Patch that is now estimated at two times the size of Texas.  Many of these long-lasting pieces wind up in the stomachs of marine birds and animals.  This results in obstruction of digestive pathways which leads to reduced appetite or even starvation.
Many chemicals undergo reactive decay or chemially change especially over long periods of time in groundwater reservoirs.  A noteworthy class of such chemicals are the chlorinated hydrocarbons such as trichloroethylene (used in industrial metal degreasing and electronics manufacturing) and tetrachloroethylene used in the dry cleaning industry (note latest advances in liquid carbon dioxide in dry cleaning that avoids all use of chemicals).  Both of these chemicals, which are carcinogens themselves, undergo partial decomposition reactions, leading to new hazardous chemicals (including dichloroethylene and vinyl chloride).
Groundwater pollution is much more difficult to abate than surface pollution because groundwater can move great distances through unseen aquifers. Non-porous aquifers such as clays partially purify water of bacteria by simple filtration (adsorption and absorption), dilution, and, in some cases, chemical reactions and biological activity: however, in some cases, the pollutants merely transform to soil contaminants. Groundwater that moves through cracks and caverns is not filtered and can be transported as easily as surface water. In fact, this can be aggravated by the human tendency to use natural sinkholes as dumps in areas of Karst topography.
There are a variety of secondary effects stemming not from the original pollutant, but a derivative condition.  Some of these secondary impacts are:
- Silt bearing surface runoff from can inhibit the penetration of sunlight through the water column, hampering photosynthesis in aquatic plants.
- Thermal pollution can induce fish kills and invasion by new thermophyllic species

# Regulatory framework
In the UK there are common law rights (civil rights) to protect the passage of water across land unfettered in either quality of quantity. Criminal laws dating back to the 16th century exercised some control over water pollution but it was not until the River (Prevention of pollution )Acts 1951 - 1961 were enacted that any systematic control over water pollution was established. These laws were strengthened and extended in the Control of Pollution Act 1984 which has since been updated and modified by a series of further acts. It is a criminal offense to either pollute a lake, river, groundwater or the sea or to discharge any liquid into such water bodies without proper authority. In England and Wales such permission can only be issued by the Environment Agency and in Scotland by SEPA.
In the USA, concern over water pollution resulted in the enactment of state anti-pollution laws in the latter half of the 19th century, and federal legislation enacted in 1899. The Refuse Act of the federal Rivers and Harbors Act of 1899 prohibits the disposal of any refuse matter from into either the nation's navigable rivers, lakes, streams, and other navigable bodies of water, or any tributary to such waters, unless one has first obtained a permit.  The Water Pollution Control Act, passed in 1948, gave authority to the Surgeon General to reduce water pollution.
Growing public awareness and concern for controlling water pollution led to enactment of the Federal Water Pollution Control Act Amendments of 1972. As amended in 1977, this law became commonly known as the Clean Water Act. The Act established the basic mechanisms for regulating contaminant discharge. It established the authority for the United States Environmental Protection Agency to implement wastewater standards for industry. The Clean Water Act also continued requirements to set water quality standards for all contaminants in surface waters. Further amplification of the Act continued including the enactment of the Great Lakes Legacy Act of 2002.