• Unit 3: Water Pollution


    After reading this unit, you will be able to:

    • define water pollution.

    • identify the main water pollutants.

    • describe the dangers of polluted water.

    • suggest the ways of preventing water pollution.



    Tap water which is considered safe for drinking sometimes includes harmful microbes. These microbes do not alter color and odor of water but are very harmful


    ACTIVITY 3.1: Showing Awareness about Water Pollution

    Investigate the level of awareness about water pollution in your area. Collect data on the sources of drinking water and polluted water from newspaper and magazines.

    What are the common water-borne diseases in the community? You can consult your local doctor/health worker for this.

    Which are the governmental and non-governmental organizations working in this field? What are the measures being taken by them for generating awareness?

    Prepare an illustrative presentation on “water pollution” from the data collected. Present it in class.

    Water is essential for life. Without water there would be no life. We usually take water as granted for its purity, but we must ensure the quality of water. Most of the water which we use comes from rivers and lakes.

    Everyday, many unwanted and harmful substances are thrown (or discharged) into the rivers and lakes. They make the water of rivers and lakes impure (or contaminated). So, we say that the water has been polluted.

    The contamination of water of rivers, lakes and ponds, etc., with unwanted and harmful substances is called water pollution.

     Water is said to be polluted when it becomes unfit for drinking or bathing. Pollution of water originates from human activities. Through different paths, pollution reaches surface or ground water. Easily identified source or place of pollution is called point source. For example, municipal and industrial discharge pipes where pollutants enter the water-source. Non-point sources of pollution are those where a source of pollution cannot be easily identified. For example, agricultural run off (from farm, animals and crop-lands), acid rain, storm-water drainage (from streets, parking lots and lawns), etc.

    3.1.1 Causes of Water Pollution

    (i) Pathogens:

    The most serious water pollutants are the disease causing agents called pathogens. Pathogens include bacteria and other organisms that enter water from domestic sewage and animal excreta. Human excreta contains bacteria such as Escherichia coli and Streptococcus faecalis which cause gastrointestinal diseases.

    (ii) Organic wastes:

    The other major water pollutant is organic matter such as leaves, grass, trash, etc. They pollute water as a consequence of run off. Excessive phytoplankton growth within water is also a cause of water pollution. These wastes are biodegradable.



    ACTIVITY 3.2: Illustrating Effects of Quantities

    Pour a cup of black ink into a river. What do you observe? Are you able to see it? Now do the same in a bucket. Do you find any change?

    When you poured a cup of black ink into a river, the ink quickly disappeared into the river’s much larger volume of clean water. The ink would still be there in the river, but in such a low concentration that you would not be able to see it. At such low levels, the chemicals in the ink probably would not present any real problem. However, when you poured a cup of ink into a bucket, the bucket quickly turned black. The chemicals in the ink could very quickly have an effect on the quality of the water.

    Thus, water pollution is all about quantities of pollutants. It depends on how much of a polluting substance is released and how big a volume of water it is released into.

    EXERCISE 3.1

     1. Most of the water which we use comes from ______ and ______ .

    2. What do you mean by water pollution?

    3. Name two pathogens which cause gastrointestinal disease.

    4. Pollution of water originates from human activities. (True or False)

    5. What are the causes of water pollution?


    ACTIVITY 3.3: Illustrating Major Pollutants of Water

    Visit your nearby water body. Collect information on the major pollutants added to the water body. Illustrate with pictures the main idea of water pollution in the water body.

    The substances which cause water pollution are known as water pollutants. Most water pollution does not begin in the water itself. For example, in oceans around 80% of pollution enters from the land. The main water pollutants are:

    3.2.1 Sewage

    ACTIVITY 3.4: Illustrating Disposal of Sewage

    Visit in groups, the sewage disposal system of your locality. Try to find out the answer to the following questions:

    • How is sewage collected from your home?

    • Where does it go thereafter?

    Sewage is a water carrying waste. It generally consists of faeces, urine and laundry waste. It also contains harmful micro-organisms such as bacteria, protozoa, fungi, viruses and parasites.


    Disposal of sewage is a big problem in developing countries. Most of the people do not have access to proper sanitation facilities. It affects people’s immediate environment causing various water-borne diseases such as diarrhea. Even if there are flush toilets, the problem still continues. When you flush the toilet, the waste has to go somewhere. Even after it leaves sewage treatment works, there is still waste to dispose off. Sometimes sewage waste is pumped untreated into the sea.

         EXERCISE 3.2

     1. Sewage generally consists of ______, ______ and ______.

    2. Disposal of sewage is not a problem in developing countries. (True or False)

    3. Name three harmful micro-organisms sewage contains.

    3.2.2 Nutrient-rich Waste Water

    The farmers use large amounts of fertilizers in the fields to increase the crop yields. These are rich in nitrates and phosphates. The excess fertilizers dissolve in water and run into rivers, lakes and ponds. Fertilizers are plant nutrients. They cause rapid growth of tiny, green, water plants called algae in the water body. Algae cover the entire water body like a green sheet. Algae compete with other organisms in the water for dissolved oxygen. As a result, there is a threat to the aquatic life.


        EXERCISE 3.3

     1. Nutrient-rich waste water causes rapid growth of green plants called ______ in the water body.

    2. Is nutrient-rich waste water a threat to aquatic life?

    3. Name the organism which covers the entire water body like a green sheet.

      3.2.3 Chemical Waste

    Almost all the industries produce poisonous chemicals as their waste products. These are called chemical waste or industrial wastes. These wastes are discharged untreated in nearby water bodies. In this way, the water bodies get polluted with chemicals. The chemicals present are the compounds of harmful metals such as mercury, cadmium, lead, arsenic and nickel. These may also include detergents and polychlorinated biphenyls (PCBs). These chemicals can kill aquatic animals and plants. They also cause severe disorders in humans such as cancer and nervous disorders.


    EXERCISE 3.4

     1. What do you mean by chemical waste?

    2. Chemical waste can cause ______ and ______ in humans.

    3. Compounds of which elements are present in chemical waste?

     3.2.4 Radioactive Waste

    ACTIVITY 3.5: Showing Radioactive Waste

    Look at the figure. Observe the sign on the dustbin. Answer the questions raised.


    Describe the picture. Make a report and submit it to your teacher.

    Radioactive waste is a waste that contains radioactive substance. A radioactive substance is unstable and produces dangerous kinds of radiation. People view radioactive waste with great alarm – and for good reason. At high concentration it can kill, at lower concentrations it causes diseases like cancer. They are carried into water from nuclear power plants, wastes of uranium and thorium during their mining and refining processes and also from medical and scientific institutions.

    EXERCISE 3.5

    1. What do you mean by radioactive substance?

    2. Radioactive waste are generated from ______ and _______ .

    3. How are radioactive wastes harmful?

      3.2.5 Oil Pollution

    Oil and oil wastes enter water bodies from different sources such as oil refineries, storage tanks, automobile waste oil, and industries. Spillage of oil from ships also results in pollution. The pollution caused by oil and oil wastes is termed as oil pollution. Oil is insoluble in water; it floats and spreads rapidly into a thin layer. This layer prevents oxygen transfer from atmosphere. As a result of this, less oxygen is available for aquatic life.



    At sea, oil layer is responsible for the death of birds. The oil penetrates the bird feathers thereby affecting their floating and flying abilities.

    EXERCISE 3.6

     1. From where do oil wastes enter into water bodies?

    2. The pollution caused by oil and oil wastes is termed ______ .

    3. How is oil pollution responsible for death of aquatic animals and plants?

    3.2.6 Plastic

    ACTIVITY 3.6:
    Say No to Plastics

    Look at the banner below. Have you seen this before? What is meant by polythene? Why and when was it banned in Rwanda? How did Rwanda accomplish it? Make a report to be presented in the class.


    Note: Polythene bags have been banned in Rwanda since 2008.

    Polythenes or polyethylenes are the most common plastics. Plastic is far and away the most common substance that washes up with the waves. There are three reasons for this: plastic is one of the most common

    materials, used for packaging, and making any kind of manufactured object from clothing to automobile parts; plastic is light and floats easily so it can travel enormous distances across the oceans; most plastics are not biodegradable (they do not break down naturally in the environment). Once in a water body they amass in landfills, litter streets, obstruct sewers and hurt aquatic life.

    A plastic bottle can survive an estimated 450 years in the ocean and plastic fishing line can last up to 600 years.

    EXERCISE 3.7

     1. ______ is the most common plastics.

    2. Plastics are biodegradable.  (True or False)

    3. Why is use of plastics prohibited?

    3.2.7 Alien Species

    Alien species (sometimes known as invasive species) are animals or plants from one region that have been introduced into a different ecosystem where they do not belong. The water hyacinth which was introduced as an ornamental plant has since invaded lakes in Rwanda.

    It has invaded from Muhazi to Rweru from the river Nyabarongo, and even reached Lake Victoria through Akagera river. The water hyacinth is a major biodiversity problem in the ecosystem of the Lake Victoria Basin.

    Rampant growth of water hyacinth can destroy native wetlands and waterways, killing native fish and other wildlife. Water hyacinth can form dense mats that spread out across water surfaces eventually choking the entire water body. Heavy weed cover also prevents the exchange of air, which normally occurs on an open water surface. This stagnation affects water quality and may result in the death of aquatic animals.


    EXERCISE 3.8

     1. What do you mean by alien species?

    2. ______ is a major biodiversity problem of the Lake Victoria Basin.

    3. Growth of ______ can destroy aquatic life.

    3.2.8 Other Forms of Pollution

    This category includes the most common forms of pollution – but by no means the only ones. Heat or Thermal pollution from factories and power plants also causes problems in the river. By adding hot water into the water body it raises the temperature. The rise in the temperature has an adverse effect on the animals and plants living in it.



    ACTIVITY 3.7: Illustrating Effects of Polluted Water

    Learners plan a field visit to nearby areas and collect various samples of water. Pour each into separate glass containers. Compare the samples for smell, acidity and color. Complete the following table in your exercise book.


    What is the possible cause of smell, acidity and color in the water? What is the possible cause of this difference? Make a comparative report of your observations.

    Acidity of water is measured as pH (power of hydrogen) of the water body. It is a figure between 0 and 14 defining how acidic or basic a body of water is along a scale. The lower the number, the more acidic the water is. The higher the number, the more basic it is. A pH of 7 is considered neutral. The pH of pure water is 7. You can use a pH strip to measure PH. The color of the strip after dipping in water will give its PH.


    Addition of pollutants to water changes its physical, chemical and biological properties. Water from different sources is likely to have different pollutants. For example, a river situated near an industry is more likely to be affected by its discharge. Water pollution is very harmful to humans, animals and water life. The effects can be catastrophic, depending on the kind of chemicals, concentrations of the pollutants and where they are polluting. Dangers of polluted water include:

    3.3.1 Eutrophication

    The entry of nutrient-rich water results in a thick growth of algae (tiny plant) called algal bloom, and many other weeds. Rapid growth of these plants covers the entire surface of water. This is called eutrophication. Eutrophication may be defined as the process of nutrient enrichment of water bodies and the subsequent overgrowth of plants on the surface of water. The algae use up a lot of oxygen that other aquatic animals die due to lack of it. It also blocks light to reach under water affecting aquatic plants. Eutrophication hence results in loss of aquatic life. Slowly, it results in the death of “lake or river”.


    3.3.2 Acidification

    The oceans are normally a natural carbon sink, absorbing carbon dioxide from the atmosphere. Carbon dioxide (CO2) is released into the oceans as a result of water pollution by nutrients. It enhances the unwanted changes in ocean acidity due to atmospheric increases in CO2. It impacts primarily the ecosystems and fish communities that live in the ocean. In particular, the rising levels of CO2 acidify the ocean. Even though the ocean can absorb carbon dioxide that originates from the atmosphere, the carbon dioxide levels are steadily increasing. The ocean’s absorbing mechanisms, due to the rising of the ocean’s temperatures, are unable to keep up with the pace. This results in acidification of oceans. Due to this, there are concerns that structures made of calcium carbonate may become vulnerable to dissolution, affecting corals and the ability of shellfish to form shells.


    3.3.3 Health Hazards

    ACTIVITY 3.8: Diseases Caused by Polluted Water

    Design a questionnaire to find out how many students in your class have been affected by one of the following diseases:


    Include in your questionnaire the cause of their disease as diagnosed by their doctors.

    Virtually all types of water pollution are harmful to the health of humans and animals. Water pollution may not damage our health immediately but can be harmful after long term exposure. People cannot survive without drinking water, and if their freshwater resources are polluted, they can fall ill by drinking them. Different types of pollutants affect human health in different ways:

    • Heavy metals from industrial processes can accumulate in nearby lakes and rivers. These are toxic to aquatic life such as fish and shellfish, and subsequently to the humans who eat them. Heavy metals can slow development; result in birth defects and some are carcinogenic, i.e., can cause cancer.

    • Industrial waste often contains many toxic compounds that damage the health of aquatic animals and those who eat them. Some of the toxins in industrial waste may only have a mild effect whereas others can be fatal. They can affect immune system, reproductive system or cause poisoning.

    • Microbial pollutants from sewage often result in water-borne diseases that infect aquatic life and terrestrial life through drinking water. Microbial pollutants include bacteria, virus and protozoa.



    Microbial water pollution is a major problem in the developing world. These illnesses are particularly dangerous for young children; in fact, they account for almost 60 per cent of early childhood deaths worldwide.


    EXERCISE 3.9

    1. Addition of pollutants to water changes its physical and chemical properties. (True or False)

    2. The pH of pure water is ______ .

    3. Water pollution is harmful to _______ and ______ .

    4. What are the dangers of water pollution? 5. Name two water-borne diseases.


    ACTIVITY 3.9: Illustrating Prevention of Water Pollution

    ‘Water water everywhere but not a drop to drink’.

    Comment on the statement given above. Make a poster/PowerPoint presentation on how you can save water. Display it in class.

    There is no easy way to solve water pollution; if there were, it would not be so much of a problem. Broadly speaking, there are three different things that can help to tackle the problem—education, laws, and economics—and they work together as a team.

    3.4.1 Education

    Making people aware of the problem is the first step towards solving it. Education can help people determine their best strategies to avoid contaminating local water sources: avoiding urinating or defecating in or near the water; building toilets/sites for waste

    downhill from wells to reduce risks of contaminating groundwater; employing household water treatment and safe storage techniques are examples. Greater public awareness can make a positive difference. Awareness helps to prevent disposal of solid and human waste and chemical and industrial waste into waterways as much as possible. It also includes treating wastes before they go into waterways.This can be achieved by setting up of educational camps.


    3.4.2 Laws

    One of the biggest problems with water pollution is its trans boundary nature. Many rivers cross countries, while seas span whole continents. Pollution discharged by factories in one country can cause problems in neighboring nations, even when they have tougher laws and higher standards. Environmental laws can make it tougher for people to pollute, but to be really effective they have to operate across national and international borders. Proper implementations of national and international laws is another issue faced by the government. Without tougher implementation it is difficult to solve the problem of water pollution. As in Rwanda, the ban of polythene is successfully implemented with inspection officers.


    3.4.3 Economics

    Most environmental experts agree that the best way to tackle pollution is through something called the 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 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, the polluter pays principle is designed to hinder people from polluting. It makes it less expensive for them to behave in an environmentally responsible way.



    Life is ultimately about choices—and so is pollution. We can live with dirty surroundings, dead rivers, and fish that are too poisonous to eat. Or 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. These actions are:

    1. Use less water:This might sound simplistic, but decreasing your water consumption is one of the keys to minimize water pollution. By reducing the amount of water you use, you will reduce the amount of water that flows into sewage treatment systems.


    2. Use environment-friendly house-hold products: Don’t use household products that contain chemicals. Instead, use green products, like biodegradable soap and all-natural toiletries.


    3. Apply natural pesticides and fertilizers: The use of chemical pesticides and fertilizers leads to water pollution because contaminated water seeps into ground water and runs off into nearby water sources.