Water pollution is defined as the presence in the groundwater of toxic chemicals and biological agents that exceed what is naturally found in water and can pose a threat to human health and / or the environment. In addition, water contamination can consist of chemicals introduced into water bodies as a result of various human activities. Any amount of these chemicals pollutes the water, regardless of the damage they may cause to human health and the environment. Water pollution is the contamination of water bodies (for example, lakes, rivers, oceans, aquifers and groundwater). This form of environmental degradation occurs when contaminants are discharged directly or indirectly into bodies of water without adequate treatment to eliminate harmful compounds.
Water pollution affects the entire biosphere of plants and organisms that live in these bodies of water, as well as organisms and plants that may be exposed to water. In almost all cases, the effect is harmful not only for individual species and populations, but also for natural biological communities. Water pollution is a major global problem that requires an ongoing evaluation and review of water resources policy at all levels (international to individual aquifers and wells). It has been suggested that water pollution is the world's leading cause of death and disease, and that it represents the death of more than 14,000 people daily. It is estimated that 580 people in India die from diseases related to water pollution every day. About 90 percent of the water in China's cities is contaminated. As of 2007, five hundred million Chinese people did not have access to drinking water. In addition to the serious problems of water pollution in developing countries, developed countries also continue to fight against pollution problems. For example, in the most recent national report on water quality in the United States, 44 percent of the miles of streams evaluated, 64 percent of the acres of lakes evaluated, and 30 percent of the bays evaluated and Estuarine square 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 known as contaminated when it is affected by anthropogenic pollutants and is not compatible with human use, such as drinking water, or undergoes a marked change in its capacity to support the biotic communities that constitute it, such as fish. Natural phenomena such as volcanoes, algae blooms, storms and earthquakes also cause important changes in water quality and the ecological status of water.