causes

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, 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. 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 includes acidity, electrical conductivity, and temperature. 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.
Contaminants may include organic and inorganic substances.
Some organic water pollutants are:
• Insecticides and herbicides, a huge range of organ halide 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.
• Detergents
• Various chemical compounds found in personal hygiene and cosmetic products
• Disinfection by-products (DBPs) found in chemically disinfected drinking water
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