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Water Pollution

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Biological Oxygen Demand

Biological oxygen demand (BOD), also known as biochemical oxygen demand, is a bioassay procedure that measures the dissolved oxygen (DO) consumed by bacteria from the decomposition of organic matter. The BOD analysis is an attempt to simulate by a laboratory test the effect that organic material in a water body will have on the DO in that water body.


The BOD test is used to measure the potential of wastewater and other waters to deplete the oxygen level of receiving waters. The test is also used to examine influents and effluents from wastewater processing facilities to compute the efficiency of operation of the treatment units.

Advantages of Water

For Humans

1. It helps create saliva.

2. It regulates your body temperature.

3. It protects your tissues, spinal cord, and joints.

4. It helps excrete waste through perspiration, urination, and defecation.

5. It helps maximize physical performance.

6. It helps prevent constipation.

7. It aids in digestion.

8. It helps with nutrient absorption.

9. It helps you lose weight.

10. It improves blood oxygen circulation.

For Other Animals

  1. Temperature Regulation

  2. pH Regulation

  3. Hydrolysis and Energy Production

  4. Digestion

  5. Joint Lubrication

For Plants

  1. Germination of seeds

  2. Helps in the process of photosynthesis

  3. Helps in the transport of nutrients and minerals from the soil to the plants

  4. Maintenance of the plant structure by providing the appropriate pressure to the plant tissues

  5. Water provides habitat in the form of ponds, rivers, lakes and sea for a large number of plants.

    Water Pollution

    Water pollution is the contamination of water bodies very often by human activities. It occurs when pollutants (particles, chemicals or substances that make water contaminated) are discharged directly or indirectly into water bodies without enough treatment to get rid of harmful compounds.

    Types of Water Pollution

    Nutrients Pollution: When too many nutrients (for example, fertilizers), mainly phosphorus and nitrogen, are added to the water, causing excessive growth of algae. When the algae die, the levels of oxygen decrease, and aquatic animals die.

    Oxygen Depletion: When too much biodegradable materials promote microorganism growth, and they use almost all oxygen in the water. All aerobic microorganisms die because of the lack of oxygen, and anaerobic organisms start producing harmful toxins such as sulfides and ammonia.

    Surface Water Pollution: When harmful substances invade water bodies such as oceans, rivers, seas, and lakes. Hazardous substances coming into contact with this surface water, dissolving or mixing with the water causes Surface Water Pollution.


    Groundwater Pollution: When humans use chemicals, pesticides and other pollutants on soils, they are washed deep into the ground by rainwater. With time, groundwater becomes completely contaminated.

    Microbiological Water Pollution: When natural bacteria and viruses affect people who drink untreated water.

    Chemical Water Pollution: When the chemicals used by farmers and industrials to control pests, weeds, and insects enter water bodies.

    Sewage Pollution: When untreated wastewater (soaps, detergents, toilet paper, cooking oil, human waste) from urban regions is discharged into a body of water such as a river, lake, stream, ocean or bay.

    Suspended Matter Pollution: When some pollutants do not dissolve in water, they remain in suspension in water. Sometimes, they end up deposited on ocean floors.

    Oil Spillage: When major offshore oil and gas drilling-related accidents result in the release of crude oil, and refined petroleum in large marine areas. Oils spills have a brutal impact on fauna, flora, and human beings.

    Ocean Dumping: When all types of radioactive, medical, industrial, toxic, domestic, and food wastes are dumped in the major bodies of water.

    Sources of Water Pollution

    There are various classifications of water pollution. The two chief sources of water pollution can be seen as Point and Non-Point.

    Non-Point: On the other hand, means pollutants emitted from multiple sources. Contaminated water after rains that has traveled through several regions may also be considered as a Non-point source of pollution.

    Point: Refers to the pollutants that belong to a single source. An example of this would be emissions from factories into the water.

    Causes of Water Pollution

    Water is uniquely vulnerable to pollution. Known as a “universal solvent,” water is able to dissolve more substances than any other liquid on earth. It’s the reason we have Kool-Aid and brilliant blue waterfalls. It’s also why water is so easily polluted. Toxic substances from farms, towns, and factories readily dissolve into and mix with it, causing water pollution.

    Mining Activities:

    Mining is the process of crushing the rock and extracting coal and other minerals from underground. These elements when extracted in the raw form contains harmful chemicals and can increase the number of toxic elements when mixed up with water which may result in health problems. Mining activities emit a large amount of metal waste and sulphides from

    Marine Dumping:

    The garbage produced by each household in the form of paper, aluminum, rubber, glass, plastic, food is collected and deposited into the sea in some countries. These items take from 2 weeks to 200 years to decompose. When such items enter the sea, they not only cause water pollution but also harm animals in the sea.

    Accidental oil leakage:

    Oil spill poses a huge concern as a large amount of oil enters into the sea and does not dissolve with water; thereby opens problem for local marine wildlife such as fish, birds and sea otters. For e.g.: a ship carrying a large quantity of oil may spill oil if met with an accident and can cause varying damage to species in the ocean depending on the quantity of oil spill, size of the ocean, the toxicity of pollutant.

    Burning of fossil fuels:

    Fossil fuels like coal and oil when burnt produce a substantial amount of ash in the atmosphere. The particles which contain toxic chemicals when mixed with water vapor result in acid rain. Also, carbon dioxide is released from the burning of fossil fuels which result in global warming.

    Leakage from sewer lines:

    A small leakage from the sewer lines can contaminate the underground water and make it unfit for the people to drink. Also, when not repaired on time, the leaking water can come on to the surface and become a breeding ground for insects and mosquitoes.

    Global warming:

    An increase in earth’s temperature due to the greenhouse effect results in global warming. It increases the water temperature and results in the death of aquatic animals and marine species which later results in water pollution.

    Industrial waste:

    Industries produce a huge amount of waste which contains toxic chemicals and pollutants which can cause air pollution and damage to us and our environment. They contain pollutants such as lead, mercury, sulfur, asbestos, nitrates, and many other harmful chemicals.

    Many industries do not have a proper waste management system and drain the waste in the fresh water which goes into rivers, canals and later into the sea. The toxic chemicals have the capability to change the color of water, increase the number of minerals, also known as eutrophication, change the temperature of water and pose a serious hazard to water organisms.

    Sewage and wastewater:

    The sewage and wastewater that is produced by each household is chemically treated and released into the sea with fresh water. The sewage water carries harmful bacteria and chemicals that can cause serious health problems. Pathogens are known as a common water pollutant; The sewers of cities house several pathogens and thereby diseases.

    Microorganisms in water are known to be causes of some very deadly diseases and become the breeding grounds for other creatures that act as carriers. These carriers inflict these diseases via various forms of contact onto an individual. A very common example of this process would be Malaria.

    Effects of Water Pollution

    Diseases: In humans, drinking or consuming polluted water in any way has many disastrous effects on our health. It causes typhoid, cholera, hepatitis and various other diseases.

    Destruction of Ecosystems: Ecosystems are extremely dynamic and respond to even small changes in the environment. Water pollution can cause an entire ecosystem to collapse if left unchecked.

    Eutrophication: Chemicals in a water body, encourage the growth of algae. These algae form a layer on top of the pond or lake. Bacteria feed on this algae and this decreases the amount of oxygen in the water body, severely affecting the aquatic life there.

    Effects the food chain: Disruption in food chains happens when toxins and pollutants in the water are consumed by aquatic animals (fish, shellfish etc) which are then consumed by humans.

    Death of Aquatic Life: Animals and plants that depend on water for life are the most affected by polluted water. Statistics from the Centre for Biological Diversity on the effects of the Deep Horizon spill provides a useful glimpse of the impact of pollution on aquatic life. In the report, the 2010 spill on the Gulf of Mexico harmed over 82,000 birds, 25,900 marine animals, 6165 sea turtles, and an unknown number of fish and invertebrates.

    Economic Effects: Managing and restoring polluted water bodies is expensive. For example, Japan declared in 2019 that it is running out of space to contain the contaminated water after the Fukushima disaster. It currently has over a million tons of contaminated water stored in tanks. Research shows that it will cost at least $660 billion to clean up the effects of the disaster.

    In normal conditions, it costs more to purify drinking water, not to mention the health cost of treating diseases resulting from contaminated water.

    Mercury Risks: Health risks from pollution vary from area to area. One of the most pervasive non-localized water pollution issues facing the world today is the level of mercury in the oceans. Inorganic mercury is a common byproduct of a number of industrial processes.

    Dangerous Mercury Levels in Fish: The level of mercury in fish is mostly dangerous for small children and women who might become pregnant, are pregnant or are nursing. Mercury has been found to interfere with the development of the central nervous system in fetuses and young children, which could potentially lead to a large amount of long-term side effects.

    Control of Water Pollution

    Save Water: Conserving water is our first aim. Water wastage is a major problem globally and we are only now waking up to the issue. Simply small changes you can make domestically will make a huge difference.

    Better treatment of sewage: So treating waste products before disposing of it in a water body helps reduce water pollution on a large scale. Agriculture or other industries can reuse this wastewater by reducing its toxic contents.

    Use environmentally friendly products: By using soluble products that do not go on to become pollutants, we can reduce the amount of water pollution caused by a household.

    Economics: Most environmental experts agree that best way to tackle pollution is through something called polluter pays principle. This means that whoever causes pollution should have to pay to clean it up, one way or another. Polluter pays can operate in all kinds of ways. It could mean that tanker owners should have to take out insurance that covers cost of oil spill cleanups, for example. It could also mean that shoppers should have to pay for their plastic grocery bags, as is now common in Ireland, to encourage recycling and minimize waste. Or it could mean that factories that use rivers must have their water inlet pipes downstream of their effluent outflow pipes, so if they cause pollution they themselves are the first people to suffer. Ultimately, polluter pays principle is designed to deter people from polluting by making it less expensive for them to behave in an environmentally responsible way.

    Our Clean Future: We can work together to keep the environment clean so the plants, animals, and people who depend on it remain healthy. We can take individual action to help reduce water pollution, for example, by using environmentally friendly detergents, not pouring oil down drains, reducing pesticides, and so on. We can take community action too, by helping out on beach cleans or litter picks to keep our rivers and seas that little bit cleaner. And we can take action as countries and continents to pass laws that will make pollution harder and the world less polluted. Working together, we can make pollution less of a problem—and the world a better place.

    Education: Making people aware of the problem is the first step to solving it. In the early 1990s, when surfers in Britain grew tired of catching illnesses from water polluted with sewage, they formed a group called Surfers Against Sewage to force governments and water companies to clean up their act. People who've grown tired of walking the world's polluted beaches often band together to organize community beach-cleaning sessions. Anglers who no longer catch so many fish have campaigned for tougher penalties against factories that pour pollution into our rivers. Greater public awareness can make a positive difference.

    Water Quality Standards

    Although pure water is rarely found in nature (because of the strong tendency of water to dissolve other substances), the characterization of water quality (i.e., clean or polluted) is a function of the intended use of the water. For example, water that is clean enough for swimming and fishing may not be clean enough for drinking and cooking. Water quality standards (limits on the amount of impurities allowed in water intended for a particular use) provide a legal framework for the prevention of water pollution of all types.


    There are several types of water quality standards. Stream standards are those that classify streams, rivers, and lakes on the basis of their maximum beneficial use; they set allowable levels of specific substances or qualities (e.g., dissolved oxygen, turbidity, pH) allowed in those bodies of water, based on their given classification.