Due to the contamination of water, How does water get polluted has become one of the rising concerns in present day. This article explains in detail how does water gets polluted.

Water gets polluted in many forms. The discharge of heated wastes affecting the thermal equilibrium existing in water (thermal pollution), discharge of chemicals (chemical pollution), discharge of suspended matter (physical pollution), discharge of pathogenic bacteria, viruses and other organisms (biological pollution) and so on are the major factors that pollute the water. Of these, the most damaging one is chemical pollution.

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How does ground-water get polluted?

The most common source of groundwater pollution in wells and springs is water from the sewage. Besides, harmful chemicals leaking from waste disposal facilities can slowly enter into groundwater reservoirs and contaminate them. Agricultural pesticides and fertilizers are also common contaminants in groundwater.

How does water get polluted on Surface Water?

Contaminants of surface water come primarily from urban, suburban, and agricultural runoff. Industrial wastes particularly those produced by the pulp and paper industries and chemical manufacturing are significant contributors. Other sources of contamination are acid precipitation; sewage and landfill leachates.

What is Thermal Pollution?

Many industrial and energy-producing processes release wastes that are warm or hot compared to the receiving environment. Excess heat or thermal pollution can harm or kill both plants and animals. When the temperature of the water rises, the amount of dissolved oxygen also decreases. Thus, another negative impact of thermal pollution is to lower the oxygen content of surface waters into which heated wastes are released.

Thus, it interferes with the physiological processes of the organisms. Fish eggs hatch much earlier in such waters and they die of starvation. Therefore, it affects the life of aquatic.

Major Factors responsible for ground-water pollution:

The Minimata Disease

The appearance of dead fish in a river is an indication of toxicity. Metals like mercury, cadmium, chromium, and lead can pollute water. Some fungicide and bactericide industries, the chlorine-alkali industry, pulp and paper, and thermometer manufacturers use mercury compounds and mercury.

The toxicity of mercury was dramatically demonstrated when during 1953, there was large scale destruction of fish around the Minimata Bay in Japan. This is famous as Minimata disease. Fish and shellfish affected by methyl mercury were eaten by villagers who were struck by a mysterious neurological illness. The waste from a nearby plastics factory causes this havoc. Many cases of congenital idiocy occurred as mothers of these children had eaten a great deal of such fish during pregnancy. This is famous as congenital Minimata disease which arises from unplanned industrialization.


Another hazardous heavy metal pollutant is cadmium. In human beings, it can produce a bizarre skeletal disorder, known as osteomalacia, which is accompanied by excruciating pain. Known in Japan as ‘itai-itai’, in the afflicted person the bones may become so fragile, that mere coughing is sufficiently traumatic to fracture the bones. Zinc smelters, industries producing pigments, plastics, stabilizers, alloys and batteries, and electro-plating industries release cadmium, as a pollutant.

Besides, lead is another metal that can act as a metabolic poison. It is cumulative in man. Automobile exhausts often release small quantities of lead into the atmosphere.


It is a toxic pollutant that can enter the rivers, lakes, and the human food chain. Coal-fired power plants are one of the largest anthropogenic sources of mercury emission. The two forms of mercury emissions are elementary mercury and mercuric chloride. Used tires and pistachio shells can clean up the pollution of mercury.

Recalcitrant Molecules

Another area of current concern is the biological effects of recalcitrant molecules. These are synthetic compounds that are not biodegradable. Therefore, it remains indefinitely in the environment. Some of them have marked toxicity to biological systems in extremely low concentrations. Examples of this type of pollutant are chlorinated hydrocarbon pesticides (like DDT), and detergents of the aryl sulfonate type. Some of the recalcitrant molecules, like polyethylene and nominated hydrocarbons, are non-toxic, but still have pollution implications; because, they are not biodegradable.

Thus, they will not decompose in the environment. Pulp and paper mills produce large amounts of an undesirable by-product, famous as lignin which is resistant to biodegradation.

Nitrate Pollution

A recent study has revealed nitric pollution of well water in many parts of our country. This pollution of well water or groundwater from shallow aquifers can be detrimental to health according to the Central Ground Water Board in Lucknow. ‘Bhu-Jal News’ published by the Board reports that it is not known which of the two main Sources – human and animal wastes or agricultural activity is responsible for this pollution. Regular monitoring of groundwater for nitrate content has become Imperative and the exact source has to be identified. Adoption of appropriate methods of collection and disposal of wastes or proper farm management techniques to prevent leaching down of nitrates to groundwater has been suggested.

Oxides of nitrogen from power stations and furnaces and vehicles aid in pollution-causing irritation of eye and breathing discomforts.

Microbe causing Water Pollution

A new microbe called Ferro plasma acidarmanus was identified as the chief suspect in the environmental damage caused by metal ore mining. It is believed to be a key mediator of the process of acid mine drainage. The microbe transforms the sulphide in metal ores into sulphuric acid, the chemical pollutant that contaminates mining sites and drains into nearby rivers, streams, and groundwater.

River Pollution

Another reason which contributes towards water polluted is the excess use of pesticides, fertilizers, and other chemicals washed by rain into streams and rivers that cause pollution.

Fourteen major rivers in India carry, among themselves, 85 percent of the surface run-off, covering 83 percent of the country within the drainage basins and house 80 percent of the population in the basin area. These, along with tanks, minor rivers, and lakes, form the sources of drinking water supply. But unfortunately, in several parts of the country, these sources are getting polluted by the discharges of community wastes and industrial effluents. The daily organic pollution load from selected large and medium industries is estimated to be equivalent to waste discharged by a population of 55 million people, according to a recent report on environmental pollution.

The River Ganga suffers from the pollution of its waters. The Central Ganga Authority (CGA) has taken up a time-bound program for setting up effluent treatment plants. Quality of the river water is being monitored, in collaboration with the Central Board for Prevention and Control of Water Pollution and State Pollution Control Boards.

Steps to reduce water pollution

NEERI (The National Environmental and Engineering Research Institute)

It was established in 1959 at Nagpur. (It was formerly known as the Central Public Health Engineering Research Institute and the name was changed in 1974). The Institute has developed low-cost sewage-treatment systems, based on pilot-plant and field-scale studies. Treatment flow Sheets have also been developed for typical industrial wastewaters from paper, textile, distillery, fertilizer, drugs, and photo film industries. Critical evaluation of water-treatment plants is also being carried out. Field studies on the water reticulation systems, with reference quality leakage and preventive maintenance, are conducted in different cities. Studies on the utilization of sewage for agriculture and aquaculture are underway. Environmental microbiology and virology are other related areas of research and interest.

The treatment of wastewaters in cold and temperate climatic regions of Europe and North America involves high energy consumption: skilled and sophisticated, mechanical process operations are needed for its execution. Besides, the predominantly tropical nature of our country favors accelerated microbial activity for degradation of biodegradable wastes, resulting in a simplified process, energy conservation, and possible reuse. The choice of technology and R&D efforts of the institute are directed accordingly.

Neeri at Nagpur has developed a low-cost technique for the production of biodegradable plastics, by using a combination of microorganism and distillery wastes. Thus, this plastic easily replaces the petrochemical-based plastics which are non-biodegradable.

Reducing Pollution Contamination

A Virginia civil engineer has developed a computer model -an improved Sequential Electron Acceptor Model 3D [SE 3D] to clean the polluted groundwater. It is designed to measure the distribution of contamination over space and time including biological reactions. Besides, it also determines how well micro-organisms respond to contaminated groundwater at each site and whether or not nature can handle the problem by itself. It is able to track each individual contaminant such as benzene, toluene, ethylbenzene, xylene, and the recently banned MTBE.


Arsenic -contaminated well water could be made safe by stirring it up with rock containing kaolinite and illite (which absorb arsenic from contaminated water). In fact, Bangladesh faces the world’s largest arsenic contamination problem. This causes a disease called Arsenism.

Inorganic arsenic is a documented human carcinogen associated with skin, liver, and lung cancers. Selenium was used to prevent the accumulation of arsenic in the human body and rectify the damages.

Water Purifying Seeds

There are certain traditional water purification techniques that are safe as per scientifically. In fact, two among them are natural coagulants such as Kataka seeds (Strychanos potatorum and Morenga olifera (drumstick).

What are the infection agents for water pollution?

Infectious agents of water are Bacteria, viruses, and other disease-causing organisms that may be found wherever human or animal wastes are among the substances contained in effluents. Measurements of the level of harmful microorganisms in the water are usually based on the abundance of Escherichia coli, which lives in the intestines of humans and some animals.

The standards for Drinking Water as per WHO

Water has become so polluted, so, WHO had laid down certain standards for drinking water. Maximum permissible chemical limits for inland surface water for public water supply – BOD Biological Oxygen Demand – 3 ppm, -pH-6-9, chloride – 600 – ppm, sulphate – 100 ppm, cyanide – 0.01 ppm, and arsenic – 0.2 ppm.

What are the effects of water pollution on Aquatic System?

Pollutants of organic and inorganic wastes decrease the dissolved oxygen (DO) content of water bodies. Contaminated water has Dissolved Oxygen (DO) below 8.0 mg/L; heavily polluted waters have 4.0 m. The amount of Dissolved Oxygen is determined by surface turbulence, consumption by organisms decomposition of organic matter and is important for the survival of aquatic organisms.

Higher amounts of organic waste increase the rate of decomposition and oxygen consumption thus reducing the Dissolved Oxygen. Demand for oxygen is directly related to the input of organic substances and is expressed as Biological Oxygen Demand (BOD). BOD is higher in polluted waters. COD (Chemical Oxygen demand), another measure of pollution refers to the measure of oxygen equivalent to the requirement for the oxidation of total organic matter.

What is Chemical Pollution?

Chemical pollution of water occurs in many ways: (i) oxygen deficiency, (ii) toxicity and (iii) eutrophication.

Oxygen from the atmosphere dissolves poorly in water, rarely reaching a level higher than ten parts per million. Yet, this remarkably small content of oxygen (dissolved) maintains a water environment viable for life. Micro-organisms in water require this dissolved oxygen for their respiration and growth. If oxygen depletes, fish may also die. The demand for dissolved oxygen is measured in two forms. They are the Chemical Oxygen Demand (COD) and the Biochemical or Biological Oxygen Demand (BOD).

Scientists have developed a process that uses bio-absorbers made from natural biological materials to bind heavy metals present in wastewater. They use thermal and membrane processes today to filter heavy metals from wastewater and return them to the production cycle.


Thus, no chemical substance is more integral to life on earth than water. Life began in the water of ancient seas, and even today we all are alive because of strict water conservation. As a vapor, it absorbs radiation to influence the heat balance and temperature of our environment; it brings moisture to the continents. As a liquid, it erodes and shapes our land, creates soil, transports minerals, and moderates climate. Of late, it is carrying millions of tons of man’s wastes out of sight. In doing so it has become polluted. Polluted water spells disaster to our biological environment.

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