The major sources of water pollution are domestic wastes, industrial wastes, agricultural, and natural. The wastes are discharged into natural bodies and chemical pesticides and fertilizers, part of which are washed and go to the water bodies. They altered the water from the natural state in physical condition, chemical and microbiological composition.

The sources of water pollution are two types; point source and non-point source of water pollution. Point sources of water pollution happen when the polluting substance is discharging directly into the water channel for example a city storm drain or a pipe spewing toxic chemicals directly into a river. A non-point source (NPS) pollution does not originate from a single discrete source. It is the collective effect of little quantity of contaminants accumulate from a big region, for instance when fertilizer from a field is carried into a stream by surface runoff.

Industrial Waste
All most all industry directly or indirectly polluted the water. The major industries such as fertilizer industries, paper industries, tanneries, food processing, textiles, and paints industries directly discharge wastes into the water bodies. Industrial processes are the main sources of the water pollution. Some of them are following:

• Many industry as like food industry and other light industries discharge non-toxic organic substances (BOD, COD).
• Thermal pollution can be occurs both human and naturally. Different industries such as power plant, nuclear power plant, nuclear weapon plants release heat into nearby water bodies for cooling purposes. Many human activities such as greenhouse effect and many industrial processes as like burning of fossil fuel are responsible for global warming. It is another reason for thermal pollution.
• Many industry releases oil, fats, grease etc into water bodies. Moreover dumping, Oil spills and shipping travel polluted the oceans.
• Different petrochemical industries discharge different petroleum hydrocarbons as like gasoline, fuel, lubricants.
• Different inorganic pollutants (as like mineral acids, Toxic metals, heavy metals, salts, acidic gas) are discharges from different industries such as automobile industry, steel manufacturing industry.
• Different organic pollutants as like plastics, fibers, elastomers, paint, elastic, plasticizer, solvents, drug, personal hygiene and cosmetic
• Many nuclear power plants, weapon plants, medicinal, industrial and research applications that use radioactive material are produced radioactive waste. Moreover mining and processing of U, Ra, Po and Th are other sources of marine nuclear waste.

Municipal Waste
The wastes from domestic households and some portion of industrial waste waters are included in municipal waste. These wastes are other significant sources of water pollution.

Sewage disposal is the main municipal waste. Frequently, it contains faeces, urine and laundry waste, flush chemical and pharmaceutical substances. It is the major problem in developing countries. Sewage often carries harmful viruses, bacteria and microorganisms.

Another municipal waste is suspended particles which is causing thick silt at the bottom. The sources of these silts are construction sites, logging, slash, burn practices or land clearing particles. Municipal waste can cause eutrophication.

Agricultural sources of water pollution
There are different fertilizers, herbicides, pesticides, defoliants, and veterinary drugs are used in agricultural purposes and these are the sources of water pollution. These compound go indo to the water bodies and polluted the water.

Fertilizers containing nutrients (nitrates and phosphates) cause excessive growth of algae and other water plants in the water bodies which is responsible for eutrophication process. Moreover some radioactive containing fertilizers are used in many farms such as tobacco farm.

Natural sources of water pollution
About 0.35% of air is carbon dioxide, moreover many industry emit huge amount of acidifying gasses, such as sulfur dioxides, nitrogen oxides and carbon monoxide. These gasses react with the rainwater and makes different acid as like sulfuric acid, carbonic acid. This acidic rain water accumulates different water bodies and changes the overall pH as well as polluted the water. It kills many vital plant lives, thereby affecting the whole food chain. Moreover when rainwater runway into water bodies, it picks up many toxic chemicals, dirt, garbage and disease-carrying organisms; this is unsafe for aquatic life.

Flood is another Natural source of water pollution. The flood water mixes with garbage, many disease-carrying organisms, chemicals, dirt and polluted the surface water.

Global warming is also responsible for water pollution. It increases the temperature of the water bodies and raises the sea levels.