Water pollution occurs when water is contaminated with chemicals and foreign substances that are harmful to humans, plants and animals. Water pollutants include chemical contamination from waste sites, chemical wastes from industrial discharges, heavy metals such as mercury and lead, sewage waste, food processing waste, fertilizers and pesticides.
Water pollution is a serious ecological threat. Drinking contaminated water is hazardous to human and animal health. When toxic substances dissolve in bodies of water, such as oceans, rivers and lakes, the water becomes polluted. Pollutants tend to lie suspended in the water or deposited on the bed. They degrade the quality of water over time. This results in disastrous effects to aquatic ecosystems. Pollutants even contaminate the groundwater, which poses a serious threat to households that use the contaminated water. Pollutants are classified into different types, including organic, inorganic and radioactive. Human activities are the main causes of pollution. The major sources of water pollution are industrial waste discharge and city sewage. These are disease-causing agents that carry bacteria, viruses and parasitic worms. Some pollutants are oxygen-demanding wastes that deplete oxygen and cause organisms in the water to die. There are also contaminants that mix with the water supply from soils and groundwater systems that contain agricultural residues and industrial wastes that are disposed of improperly. Contaminants from the atmosphere also enter groundwater systems through rainfall.