What are Water Pollutants? – Definition, Sources and Types

What are Water Pollutants? – Definition, Sources and Types

Water Pollutants kill more people every year than from all forms of violence including war, according to the UNDESA. Every day, 2 million tons of sewage, industrial, and agricultural waste reaches water bodies all over the world. With the growth of the human population, industrial and agricultural activities the hydrological cycle got disrupted. As a result, declining water quality has become a global issue of concern.

In this blog, I will take you on a short trip exploring the various water pollutants, its sources and effects.

Water Pollutants Definition

Water Pollutants are the organic or inorganic chemicals and microbes that degrade the water quality of a water body and renders it hazardous for human consumption and the aquatic life thriving in it. Toxic compounds from farms, cities, and factories easily dissolve and combine with it, polluting the water.

Water, also known as a “universal solvent,” can dissolve more chemicals than any other liquid on the planet. It’s also the reason why water gets easily polluted.

Water pollution
Water pollution

Water Pollutants Sources

The sources of water pollutants belong to two categories.

  • Point Source Water Pollutants
  • Non-Point source Water Pollutants

Point Source Water Pollutants

Point source water pollution occurs when contamination arises from a single source. Examples of point source water pollutants include contamination from leaking septic systems, chemical and oil spills, effluent released illegally by an oil refinery, or wastewater treatment plant . While point source water pollutants originate in a single location, it has the potential to pollute miles of streams and the ocean.

Non-Point Source Water Pollutants

Water Pollutants arising from dispersed sources is referred to as non point source water pollutants. Agricultural or storm water runoff, pond ash from ash dykes, as well as debris blown into streams from land, are examples. Above all, it’s tough to control because there’s no single, recognisable source.

Water Pollutants Types

Water Pollutants are classified into nine types as shown below.

  • Oxygen Demanding Wastes
  • Disease-causing Agents
  • Synthetic Organic Compounds
  • Plant Nutrients
  • Inorganic Chemicals and Minerals
  • Sediments
  • Radioactive Substances
  • Thermal Discharges
  • Oil

Oxygen Demanding Wastes

  • Organic wastes which demand a high amount of dissolved oxygen for their microbial decomposition are referred to as oxygen demanding wastes.
  • Such kind of organic wastes arises from sewage, food processing plants, tanning operations etc.
  • Biochemical Oxygen Demand or BOD measures the water pollution potential of the organic waste.
  • The amount of dissolved oxygen (DO) required by aerobic biological organisms to decompose the organic waste present in a given water sample at a particular temperature over a given time period is known as biochemical oxygen demand (BOD).
  • Oxygen demand is directly proportional to the organic waste concentration in the water.
  • In other words, the higher the BOD of the wastewater, the higher is the amount of oxygen required for the degradation of waste.
  • Oxygen demanding wastes pose a hazard to aquatic life by using up the dissolved oxygen in the water for its degradation.
Water pollution effects on aquatic life
Water pollution effects on aquatic life

Disease-causing Agents

Sewage and wastes from farms and industries like tanning and meat packaging industries carry pathogens into the water bodies. As a result, water contains bacteria which causes cholera, typhoid, amoebic dysentery and viruses responsible for polio, coxsackie fever. These pathogens enter the human body through drinking water and other activities.

Escherichia coli is a harmless bacteria found in high concentrations in human faeces. They are used to assess the hygienic quality of water. Since the coliforms usually travel together with the pathogens, a high concentration of E. coli indicates faecal contamination and the presence of pathogens.

Synthetic Organic Compounds

  • Pesticides, insecticides and herbicides used in the crop fields reach the water bodies via surface runoff from agricultural lands and stormwater.
  • The commonly used chlorinated pesticides include aldrin, dieldrin and DDT.
  • They are highly stable, volatile and soluble in fats and oils and they accumulate in the bodies of aquatic organisms.
  • Through biological magnification, it gets more concentrated from one trophic level to the next in the food chain.
  • Fishes and predatory birds are the victims of pesticide pollution. For instance, dieldrin affects the calcium metabolism in predatory birds and leads to thinning of their eggshells.
  • Through drinking water and consumption of fishes, pesticide residues enter the human body.
  • The surfactants present in detergents create foam in water bodies and hamper the oxygen absorption of water. And, higher levels of phosphate act as a plant nutrient and generate eutrophic conditions.

Plant Nutrients

  • Phosphates, nitrates and ammonia are the major plant nutrients. They find their way into water bodies via effluents from fertilizer, food and textile industries.
  • As the concentration of these nutrients increases in the water bodies, algae absorbs them and grows excessively, resulting in eutrophication.
  • The process through which a water body gets enriched in dissolved nutrients is known as eutrophication.
  • This leads to algal bloom and develops a green slime layer over the surface of the water.
  • Therefore, sunlight can’t reach the bottom of the water bodies and this hampers atmospheric reoxygenation.
  • After that, the algal growth dies down and its degradation results in anaerobic conditions.
  • An anaerobic bacterium, Clostridium botulinum can flourish in this environment. It secretes a powerful toxin, botulinum that kills the algae feeding birds and humans.
  • Nitrate enters the human body through drinking water. It forms a complex, methaemoglobin which reduces the oxygen-carrying capacity of the blood. This leads to a fatal condition called methaemoglobin anaemia or blue baby disease.

Inorganic Chemicals and Minerals

The water pollutants like inorganic salts, mineral acids, finely divided metals and metal compounds fall under the category of inorganic chemicals and minerals. Municipal and industrial wastewater and mine runoffs are the main sources of these pollutants. Sulphur and coal mining leads to acid mine drainage consisting of sulphuric acid and iron compounds. In addition to this, tanneries, textiles and coke oven operations release alkalies to the water bodies.

  • Cadmium, Chromium, Lead, Mercury and Silver are metals found in industrial wastewater that requires serious attention.
  • Effluents from chemical plants, electroplating and textiles generate cadmium. The use of cadmium contaminated water for irrigation may have been the reason for itai-itai disease in Japan.
  • Wastewaters from aluminium anodizing, paint and dye industries, ceramic and glass industry brings both trivalent and hexavalent chromium to the water bodies.
  • Lead is present in industrial effluents from battery manufacture, printing and painting operations. It is a cumulative poison and concentrates mainly on the bones.
  • The most toxic aquatic pollutant is mercury owing to its rapid methylation in the aquatic environment. It builds up in the food chain and reaches toxic levels at the top of the trophic level.
  • Severe mercury poisoning causes Minamata disease, a neurological disease. Industrial effluents from chlorine and caustic soda, fertilizers and pesticides are the main culprits of mercury pollution.
  • The main sources of silver in wastewater are electroplating and photographic operations.
Water Pollution by chemicals
Water Pollution by chemicals


Soil, sand and mineral particles reaching the aquatic environment through floodwaters constitute the sediments. The presence of sediments increases the turbidity of water bodies. Therefore, sunlight can’t penetrate to the bottom and its availability to aquatic plants decreases. Moreover, they cause the thickening of fish gills and asphyxiation of the fish and sediments also destroy the spawning sites of fish on the river bed.

Radioactive Substances

The radioactive material used in industrial, medical, or scientific activities creates nuclear waste. Uranium and thorium mining and refining are also sources of nuclear waste. Radium is the most important radioactive waste product and is a health hazard in drinking water.

Thermal Discharges

  • Heat is a water pollutant because it reduces the capacity of water to carry dissolved oxygen and raises the rate of metabolism in fish.
  • The practice of releasing cooling water from power stations into rivers is a major source of heat since the released water can be up to 15 degrees Celsius warmer than naturally occurring water.
  • Firstly, some fish species, such as trout, cannot survive in water with very low dissolved oxygen levels. Secondly, their eggs will not hatch at temperatures higher than 14.5 degree Celsius.
  • Moreover, there is a decline in oxygen saturation percentage with the increase in temperature.
  • Due to the density difference, hot water forms a separate layer above cold water.
  • This prevents the reaeration of the cold water underneath, as it has no atmospheric contact.
  • Due to the normal biological activities in the lower layer, the Dissolved Oxygen level falls rapidly and generates anaerobic conditions.


Every year, nearly half of the estimated 1 million tonnes of oil that enters marine habitats comes from land-based sources such as factories, farms, and towns. In addition, oil can ooze out from the ocean’s depths and eroded sedimentary rocks. Since oil does not dissolve in water and instead forms a thick sludge, it suffocates fish and sticks to the feathers of marine birds, preventing them from flying. Also, it prevents photosynthetic aquatic plants from receiving sunlight.

water pollution
water pollution

To sum up, the concentration of pollutants in water can be reduced by treating the effluents. To know more about wastewater treatment methods, please check our blogs, Wastewater Treatment- Stages and Process full details.

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