What is Water Pollution? Causes, Sources, Effects and Control Measures

What is Water Pollution? Causes, Sources, Effects and Control Measures

Water Pollution - Introduction

Water pollution contaminates water sources including ponds, lakes, rivers, groundwater and the ocean. Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without removing harmful compounds. Water pollution affects plants and organisms living in these bodies of water and human communities that use the polluted water. 

Here are some UN statistics  and facts on water pollution: 

  • The major sources of water pollution are human settlements and industrial and agricultural activities.
  • Every day, 2 million tonnes of human waste are disposed of in water bodies.
  •  At least 1.8 billion people worldwide are estimated to drink faecally contaminated water. An even greater number drink water delivered through a system without adequate protection against sanitary hazards.
  • In developing countries, 70% of industrial wastes are dumped untreated into waters where they pollute the usable water supply
  • Nitrate from agriculture is the most common chemical contaminant in the world’s groundwater aquifers. 
  • Half of the world’s wetlands, which act as natural filters, have been lost since 1900.   

What are the Pollutants of fresh Water and what are the effects? 

Most of the freshwater sources in the world like rivers, lakes, and groundwater are already polluted. This is true even in remote places like the polar regions. Most of the pollution that ultimately reaches the ocean contaminates freshwater sources. 

The main categories of water pollutants and their effects are: 

  • Sediments: Excessive amounts of soil particles carried by flowing water, when there is severe soil erosion. Sediments cloud the water and reduce photosynthesis, clog reservoirs and channels, smother coral reefs, destroy the feeding grounds of fish, and disrupt aquatic food webs. 
  • Oxygen-demanding wastes: Organic wastes such as animal manure and plant debris decomposed by bacteria, from sewage, animal feedlots, paper mills, and food processing facilities. Bacteria that decompose these wastes deplete the oxygen and cause the death of fish and other aquatic organisms. 
  • Infectious Microorganisms: Parasitic worms, viruses, and bacteria from infected organisms as well as human and animal wastes. They are responsible for water-borne diseases that kill thousands of adults and children, primarily in developing countries.
  • Organic compounds: Synthetic chemicals containing carbon from industrial effluents, surface runoff, and cleaning agents. These chemicals cause many health problems for humans and harm fish and wildlife.
  • Inorganic nutrients include nitrogen and phosphorus from animal waste, plant residues, and fertilizer runoff. The nutrients can cause eutrophication and can affect infants and unborn babies. 
  • Inorganic chemicals: Acids, salts, and heavy metals like lead and mercury from industrial effluents, surface runoff, and household cleaning agents. They make water unfit for drinking or irrigation, harm fish and other aquatic organisms, cause many health problems for humans, and lower crop yields. 
  • Radioactive substances: Wastes from nuclear power plants, nuclear weapons production, and mining and refining uranium and other ores. Such substances cause cancers, birth defects, miscarriages, etc.  
  • Thermal Pollution: Hot water from industrial processes. That heat lower oxygen levels and makes aquatic organisms more vulnerable to disease, parasites, and toxic chemicals. When the hot water is let in, the sudden increase in temperature produces thermal shock in aquatic organisms. 

Sources of Water pollution  

Major sources of water pollution are as below: 

  • Domestic Sewage: Humans use water for drinking, cooking, washing clothes, gardening, recreation, etc. The discharged water has soluble and insoluble, organic and inorganic matter. It includes detergents, toxic heavy metals and even pathogens. In the municipal drains, the domestic sewage is mixed up with garbage from urban and rural settlements. This highly polluted water is discharged into rivers, lakes and ponds. Thus domestic waste and garbage are the main sources of water pollution. 
  • Industrial Waste: Industrial wastes are the most harmful of all water pollutants as they contain toxic metals (lead, mercury, zinc, copper, chromium and cadmium) and toxic non-metals (arsenic, acids, alkalis, cellulose fibres, colouring and bleaching materials, petrochemicals, etc.). These pollutants are continuously discharged into the water bodies either directly or from waste dumps.
  • Agricultural Waste: Water pollution caused by agriculture is mainly an outcome of fertilizers and agricultural chemicals such as insecticides and herbicides that run off into streams and lakes. They are rich in many nutrients and lead to phenomena like eutrophication. 
  • Off-shore Oil Drilling: This pollution is mainly due to the loss of oil during off-shore exploration, oil drilling and extraction of mineral oil, leakage of oil and natural gas from underwater pipelines and oil spills from oil tankers. The waste oil also reaches the oceans and seas due to leakage during the loading and unloading of oil tankers, runoff from the roads at seaports and washing of oil tankers.
  • Thermal Pollution: Most of the large-scale industrial units, thermal power plants, nuclear power plants, oil refineries, etc., are located along the banks of rivers. These industries use large quantities of fresh water for cooling purposes. The hot water is generally discharged into the rivers. This increases the temperature of river water by about 10 Degrees Celcius, and this leads to thermal pollution of water. This has a harmful effect on aquatic organisms, such as fish and algae. The increase in the temperature of river water also decreases the level of dissolved oxygen, which results in the release of foul and toxic gases.    

Some Forms of Water Pollution:-

1. Eutrophication

Eutrophication is defined as an increase of plant nutrients particularly nitrogen and phosphorus in water bodies. Natural eutrophication occurs naturally when a lake or river ages over a period of hundreds or thousands of years, Human activities release excess amounts of nutrients in water bodies. This causes eutrophication. This type of eutrophication is called cultural eutrophication. 

Sources of Eutrophication: 

  • Natural sources of nitrogen and phosphorus are biogeochemical cycles i.e. nitrogen and phosphorus cycles 
  • Phosphorus and nitrogen deposition occurs through rainfall in water bodies.
  • Agriculture is the major source of eutrophication of freshwater. Fertilizers rich in nitrogen and phosphorus deposit large amounts of nutrients in the soil. Runoffs and erosions from these farms cause eutrophication in water bodies. The other main source is domestic animal farming. 
  • Fossil fuel-burning processes in industries are important sources of nitrogen oxides. These are carried down by rainfall to water bodies. This causes eutrophication.
  • The sewage treatment process releases oxides of nitrogen and phosphorus. This drains into water bodies causing eutrophication. Household detergents, often have high phosphate content. These are also drained into sewage.
  • Motor vehicles release nitrogen oxides. These are carried down by rainfall to water bodies. This also causes eutrophication.  

Effects of Eutrophication: 

  • When there is an increase in nutrients in lakes, algae grow fast and use up lots of oxygen. The growth of excess algae harms water quality. It decreases the dissolved oxygen in the water. This gives water a bad smell and a green or blue-green colour. 
  • Fish die due to a lack of dissolved oxygen. Most of the invertebrates in water die if oxygen levels fall below 4-5 mg/l for long periods of time.
  • Some algal blooms produce toxins like microcystin and anatoxin-a. These are very harmful to aquatic plants and animals. These toxic chemicals can enter the food chain. These can cause poisoning in domestic animals, wildlife and human beings. 

Control of Eutrophication  

  • Phosphorus can be removed by the addition of a chemical that precipitates phosphate. This occurs by chemical reaction. Nitrogen can be removed by microorganism activity. Nitrogen removal costs more money. It is more difficult to remove than phosphorus. 
  • Controlling the use of fertilizers. Using organic farming can also help to control eutrophication. 
  • Wetlands are sometimes used to solve the problem of eutrophication. Both nitrogen and phosphorus may be removed by wetlands. Nitrate is converted in wetlands to free nitrogen and released into the air. Phosphorus is adsorbed by wetland soils and is taken up by plants.
  • Nitrogen in rainwater can be decreased by controlling air pollution in the area. 
  • Careful planning and management should be done for lakes used for fish culture. 

2. Harmful Algal Blooms (HABs) 

HABs are large colonies of algae and other photosynthetic organisms proliferate uncontrollably in oceans, brackish water or freshwater water bodies. They affect oceans and other water bodies like ponds, rivers, streams, lakes, and even reservoirs. They are caused by various photosynthetic organisms, like toxic phytoplankton, cyanobacteria ( cyanobacteria are microscopic organisms that do photosynthesis in aquatic ecosystems), micro-algae, benthic algae and macro-algae. These algal blooms may be blue-green, red, brown or yellow in colour. Thus, red tide is one type of HAB.

The major impacts of HABs are: 

  • Such blooms produce toxins that can kill mammals, fishes, birds and other organisms. Toxins of HABs can contaminate food webs and also cause human illness or death in extreme cases.
  • Some algae are non-toxic but consume all the dissolved oxygen in the water. Such regions with depleted oxygen levels are called Hypoxic zones which aren’t able to sustain life. Thus, dead zones in water may be created where aquatic life cannot survive. Hypoxia means “Low Oxygen.” In aquatic ecosystems, low oxygen usually means a concentration of less than 2-3 milligrams of oxygen per litre of water (mg/L). A complete lack of oxygen (omg/L) is called Anoxia. 
  • Algae may also smother corals and block the sunlight availability for the coral reef ecosystem thus affecting the health of the coral reef ecosystem. 
  • Some algae may discolour water and contaminate drinking water.        

HABs can occur both due to natural and human-induced factors. Aaaaincreased nutrient discharge, mainly phosphorous and nitrogen, from agricultural runoff and untreated sewage can be a major driver of HABs. Apart from this, food web alterations exotic species, changes in the water flow and climate change all play a role in HABs. 

Water Pollution Due to the Toxic Elements and Their Effects:-  

1. LEAD 

Sources of lead in water 

  • Lead processing plants working with lead ores
  • Production of lead-acid batteries. 
  • Lead pipes: Lead is found in drinking water from plumbing. 
  • Lead-contaminated soil: Plants take up high levels of lead up to 500 ppm from contaminated soil. Thus, lead enters the food chain. It affects each member of the chain.
  • Organic lead is used in petroleum industries and inorganic lead compounds for battery and paint production.
  • Lead smelters, household dust etc also add lead to water. 

Harmful effects of lead as a water pollutant 

  • Lead poisoning causes headaches, depression, nausea, muscle pain, loss of appetite etc. High doses of lead cause colics, abdominal pain, memory loss, kidney failure, skin pigmentation and even paralysis.
  • Lead pollution can damage internal organs, especially the brain, nervous and reproductive systems. Organic lead products may be cancer-causing also.
  • Women and children are more affected by lead poisoning than men. Lead causes menstrual disorders and infertility. It increases the risk of stillbirth. In children, it can cause learning problems and mental retardation. 
  • Lead poisoning decreases wild bird populations.


Sources of mercury in water 

  • Mining of mercury ores 
  • Use of mercury in products and manufacturing, production of zinc, steel and other metals.
  • Coal-fired power plants where burning of coal releases mercury.
  • Use mercury in industries to prepare thermometers, pressure gauges, electric switches, fluorescent lamps, and dental fillings. 
  • Use Of  Inorganic mercury compounds in batteries, paper manufacturing and the chemical industries.
  • Release of mercury naturally present in limestone, coal, crude oil, metal ores, volcanic eruptions etc. 
  • Mercury present in the atmosphere enters lakes and other water bodies through rain and snow. 

Harmful effects of mercury as a water pollutant 

  • When mercury is deposited in lakes or waterways, bacteria convert it to methylmercury. Methyl Mercury deposits in algae and is eaten by smaller fish, which are eaten by larger fish. Mercury present in fish is eaten by humans or other wildlife. Methyl mercury is able to enter our blood and organs. It can damage the brain and nervous system. 
  • Acute mercury poisoning can lead to depression, Suicidal tendencies, Paralysis, Kidney failure, Allergies 
  • Minamata disease in Japan was caused due to mercury poisoning. 
  • Children and Pregnant women are more affected by mercury. Inorganic mercury is easily absorbed into the bodies of children. 
  • Some people show allergic responses to tiny amounts of mercury.


Sources of cadmium in water 

  • Corrosion of galvanized pipes when soft water with low pH passes through these pipes. 
  • Erosion of natural deposits,
  • Discharge from metal refineries 
  • Runoff from waste batteries and paints. 
  • Metal processing (Zinc, aluminium, iron and steel) industries 
  • Mine waters 
  • Battery recycling plants
  • Coal and oil combustion in power plants 
  • Use of cadmium for metal plating, coating, making transportation equipment, machinery and baking enamels, photography, nickel-cadmium solar batteries and pigments. 
  • Use of cadmium sulphide as pigments in plastics. 

Harmful effects of cadmium as a water pollutant 

  • Cadmium deposits in fish. When human beings eat fish, cadmium is absorbed. It binds to a low molecular weight protein metallothionein in the liver, kidney, intestine and pancreas. Kidneys are most affected by cadmium poisoning. Kidney stones are formed. 
  • Cadmium poisoning causes the following; Nausea, Vomiting, Diarrhoea, Muscle cramps and loss of calcium from bones,  Yellow colouration of teeth, Decrease of red blood cells, Damage of bone marrow, Hypertension, Kidney failure, and Lung irritation. 
  • Itai Itai is caused by cadmium contamination associated with a diet low in calcium and vitamin D. It is osteomalacia and severe urinary system disease. 
  • Cadmium compounds can also cause various types of cancer.


Sources of Arsenic in water 

  • Arsenic occurs in more than 200 minerals mainly as arsenopyrite (FeAsS) and other sulfide minerals. Arsenic is found as local bedrock mainly in Bangladesh, West Bengal (India) and some regions of China. In all these areas, arsenic occurs in deltaic alluvial sediments in shallow aquifers. These are the main sources of groundwater arsenic pollution.
  • Erosion of natural deposits, 
  • Runoffs from glass and electronics production wastes 
  • Industrial effluents.
  • Agricultural, mining and smelting activities. 
  • Weathering of rocks and minerals followed by leaching and runoff. Igneous rocks formed from volcanoes have high arsenic content. 
  • Igneous rocks formed from volcanoes have high arsenic content. 

Harmful effects of arsenic in water 

  • Arsenic in drinking water causes bladder, lung and skin cancer. It may also cause kidney and liver cancer. 
  • Arsenic causes serious skin problems. 
  • Arsenic harms the central and peripheral nervous systems. 
  • It affects the heart and blood vessels.
  • It also may lead to birth defects and reproductive problems.
  • Keratosis on the palms of the hands and sores of the feet 
  • Black foot disease, 
  • Cardiovascular disease, Bone marrow depression 
  • Arsenic is harmful to the liver and causes cirrhosis of the liver sometimes. 

How does Groundwater Get Polluted? 

About 2 billion people, approximately one-third of the world’s population, depend on groundwater for their daily needs. About 600 cubic km of groundwater is withdrawn every year, mostly from shallow aquifers. 

It was believed for long that water that slowly seeps or infiltrates into the ground would be thoroughly filtered by the soil and hence groundwater would be free of pollutants. We know now that this is not necessarily true. The filtering capacity of soil varies greatly from place to place. Further, there is also a limit to the amount of pollutants the soil can filter. 

Excessive extraction leads to the natural pollution of groundwater. Example- fluoride concentration. In coastal areas, when water tables drop due to excessive extraction, there is intrusion of salt water and this is often an irreversible process.

Groundwater receives pollutants from septic tanks, landfills, hazardous waste dumps, and underground tanks containing petrol, oil, chemicals, etc. Substances like paint thinners and motor oil that we pour on the ground ultimately reach the groundwater. 

Groundwater pollution is long-lasting because it does not get flushed or decomposed away. The flow of groundwater is very slow, decomposing bacteria are few in number, and the cold temperatures slow down the decomposing process. As a result, even degradable waste stays in the water for hundreds to thousands of years. In any case, non-degradable waste like lead, arsenic, and fluoride remains in groundwater permanently.  

What are the effects of the decrease in the pH value of water? 

pH of water bodies depends on both natural and human factors. When rainwater falls through the air, gases such as carbon dioxide dissolve in rainwater and form carbonic acid. Therefore, rainwater is slightly acidic in nature. It has a pH value of 5-6 

Water organisms can live in pH values of about 5.0 to 9.0. Fishes prefer waters between 6.0 and 8.2. The suitable pH for most aquatic organisms is 6.0 

  • Sulphur dioxide and nitrogen oxide form sulphuric acid and nitric acid. These mix with rainwater to form acid rain. pH of water falls to 4 or lower due to acid rain. It kills fish and many aquatic animals. It decreases crop production. Historical buildings are blackened due to acid rain. 
  •  Mining operations also add acids to water. Metals such as iron, cadmium, lead, and chromium atc dissolve more easily in acidic water. Many heavy metals become toxic when dissolved in water. This causes water pollution. 
  • Bacteria and fungi decrease in acidified water. This decreases the rate of decomposition of organic matter. As a result, nutrient cycling is disturbed. 

Water Pollution Control and Abatement  

The main objectives of wastewater treatment are as follows 

To remove pollutants from water.

To produce a waste stream called effluent

To produce solid waste 

To discharge or reuse the solid waste and waste stream safely into the environment.

Wastewater treatment operates in the following four sequences:

  1. Pretreatment: Large solids such as plastics, sticks, rags, leaves, branches etc are present in wastewater. These can be easily removed during pretreatment. Pretreatment involves screens made of metal bars. Solids are then collected and disposed of in a landfill.
  2. Primary treatment: In the primary treatment process, different types of tanks, grinders and separators are used. It uses a screening process, comminutor, grit chamber and skimmers.

In the screening process, plastic, branches, rags, metals etc are caught in some screens.

A comminutor is a grinding pump. It contains a rotating cutting screen. This cutting screen cuts large chunks of organic matter in the wastewater into small pieces. 

In a grit chamber, pieces of grit materials like rock, metal, bone etc are allowed to settle out of the waste stream.

Skimmers remove floating oil and grease from the wastewater. After these steps, sedimentation is carried out in sedimentation tanks also called primary clarifiers to remove the waste materials. After the primary treatment process, the secondary treatment is carried out.

3. Secondary treatment - Secondary treatment process mainly involves the biological treatment process. Microorganisms degrade the biological content (dissolved organic matter) of the sewage. In this process, air is blown over the sewage to increase the growth of aerobic bacteria and other microorganisms.

These bacteria need oxygen. These microorganisms oxidize the dissolved organic matter to carbon dioxide and water.

4. Tertiary treatment: Any level of treatment beyond the secondary treatment processes is tertiary water treatment. This involves different physical and chemical processes. Nutrients such as nitrogen and phosphorus, non-biodegradable organic pollutants, toxic chemicals, metals and additional suspended solids are removed by this process. 

There is another way to control water pollution and that is 

Remediation - This means cleaning up natural water streams like rivers, lakes, groundwater etc. after they have been polluted. Although it is much more expensive than reducing pollutant input or wastewater treatment before discharge, it is sometimes the only option. For example - Groundwater can be treated with microbes to decompose organic pollutants. 

Lake acidity caused by acid rain can be treated with chemical bases such as lime. Lime is disseminated in the lake to neutralise acidity 

Frequently Asked Question 

Question: What is Water Pollution?

Answer - Water pollution may be defined as any chemical or physical change in water, detrimental to living organisms. It can occur through natural processes, for example by sediments produced by natural erosion. Waterbodies are a major recipient of an extensive array of wastes produced by human activity. These may be discharged directly into watercourses by sewers or pipes from factories or be washed down (run-off) from agricultural or urban areas, particularly after heavy rains. Under rather exceptional circumstances, waterbodies may become significantly contaminated by the atmospheric deposition of pollutants. 

Question: What is Eutrophication?

Answer - It is the process by which a body of water develops a high concentration of nutrients, such as nitrogen and phosphorous resulting in abundant plant and algal growth.

Question: What is Thermal Pollution of Water?

Answer - Thermal pollution is defined as a sudden increase or decrease in the temperature of any natural body of water, which is caused by human activity. This normally occurs when a plant or facility takes in water from a natural resource and puts it back with an altered temperature. Most often, water is used as a coolant and hence the discharged water is at a higher temperature.

Question: What is the impact of thermal pollution?

Answer - Thermal pollution has negative effects such as the following:

  • Decrease in the levels of dissolved oxygen in water, which can suffocate species. An example is the mass of fish kills seen in some water bodies.
  • Loss of biodiversity because some species cannot tolerate the higher water temperatures - their reproductive systems are affected and they migrate to other areas. 

Question: What is Biological Oxygen Demand?

Answer - It is the amount of oxygen required for the biochemical decomposition of dead organic matter in a water body. It is measured in parts per million or ppm.

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