Water pollution is the contamination of bodies of water (eg lakes, rivers, oceans, aquifers and groundwater). This form of environmental degradation occurs when pollutants are discharged directly or indirectly into bodies of water without adequate treatment to remove harmful compounds. Water pollution affects the entire biosphere - plants and organisms that live in these bodies of water. In almost all cases the effect damages not only individual species and populations, but also natural biological communities.
Water pollution is a major global problem requiring the ongoing evaluation and review of water resources policy at all levels (international to aquifers and individual wells). It has been suggested that water pollution is the leading global cause of death and disease and accounts for the deaths of more than 14,000 people daily. It is estimated that 580 people die in India from diseases related to water pollution every day. About 90 percent of the water in China's cities is polluted. As of 2007, half a billion Chinese had no access to safe drinking water. In addition to the acute problems of water pollution in developing countries, developed countries also continue to struggle against pollution problems. For example, in the most recent national water quality report in the United States, 44 percent of miles assessed, 64 percent of assessed acres and 30 percent of assessed bays and estuarine miles were Classified as contaminated. The head of China's national development agency said in 2007 that a quarter of the length of China's seven major rivers were so poisoned that water damaged the skin.
Water is typically referred to as contaminated when it is damaged by anthropogenic contaminants and does not withstand human use, such as drinking water, or experiences a marked change in its ability to support its constitutive biotic communities, such as fish. Natural phenomena such as volcanoes, algal blooms, storms and earthquakes also cause major changes in water quality and the ecological status of water.
Causes
Specific contaminants leading to contamination in water include a broad spectrum of chemicals, pathogens, and physical changes such as elevated temperature and discoloration. While many of the chemicals and controlled substances can be natural (calcium, sodium, iron, manganese, etc.), concentration is often the key to determining what is a natural component of water and what is a contaminant. High concentrations of natural substances can have negative impacts on aquatic flora and fauna.
Substances that deplete oxygen can be natural materials such as vegetable matter (eg leaves and grass) as well as man-made chemicals. Other natural and anthropogenic substances can cause turbidity (cloudiness) that blocks light and disrupts plant growth, and obstructs the gills of some species of fish.
Many of the chemicals are toxic. Pathogens can cause waterborne diseases in human or animal hosts. The alteration of the physical chemistry of water includes acidity (pH change), electrical conductivity, temperature and eutrophication. Eutrophication is an increase in the concentration of chemical nutrients in an ecosystem to an extent that increases the primary productivity of the ecosystem. Depending on the degree of eutrophication, subsequent negative environmental effects, such as anoxia (oxygen depletion) and severe reductions in water quality may occur, affecting fish and other animal populations.
