Natural Resources

Tutormate > CBSE Syllabus-Class 9th Biology > Natural Resources

5 Water Pollution

  • Oceans, rivers, streams, lakes, ponds, polar ice caps, water vapour, etc., collectively form the hydrosphere.
  • Water is one of the most unusual natural compounds found on Earth and it is also one of the most important substances.
  • Water in some form or the other is essential for the maintenance of all life.
  • Water sources need to be easily accessible to animals and plants to survive on land. Availability of water decides not only the number of individuals of each species that are able to survive in a particular area, but it also decides the diversity of life there.


Rain water harvesting is the technique used to capture, store and reutilize rain water, by making special water-harvesting structures such as dug-out wells, percolation pits, check dams, and lagoons

Advantages of Rain-water Harvesting:

  • Rain-water Harvesting reduces the run-off loss of rain water.
  • Rain-water Harvesting helps to raise the water table.
  • Rain-water Harvesting checks soil erosion.
  • Rain-water Harvesting is helpful in controlling foods.
  • Rain-water Harvesting maintains a supply of water during the dry months of the year.

Conservation and Management of Water Resources:

Measures for avoiding misuse and wastage of potable water:

  • Adoption of various food control methods.
  • To identify the over exploited areas of fresh water, extensive hydrogeological surveys are done.
  • To avoid wastage and misuse of water, there is an urgent need of mass awareness programmes through public and private agencies.
  • The ground water is recharged by artificial means.

Water pollution:

  • The addition of undesirable substances to water bodies such as lakes, rivers, oceans, underground water and seas, removal of desirable substances from water bodies (e.g., removal of dissolved oxygen) and change in temperature cause water pollution.
  • The major pollutants are usually lead, mercury, fertilizer and pesticide compounds.
  • For example the major source of pollution of the Ganga River is sewage and industrial wastes from tanning factories.
  • Polluted water becomes unfit for drinking, bathing, washing and irrigation.

Types of water pollution:

Water pollution is of following three types:

  • Surface water pollution (or Inland water pollution);
  • Underground water pollution;
  • Marine water pollution.

Types of water pollutants:

  • Physical water pollutants
    Physical water pollutants include heat and oil-spills.
  • Thermal Pollution:
    Specific industries and thermal/nuclear power plants use water for cooling in various operations and later return this hot water to water bodies. This results in thermal pollution.
  • Chemical water pollutants
    Chemical water pollutants include pesticides (e.g., dieldrin, DDT, DDE, BHC, etc.), organic wastages (e.g., sewage), polychlorinated biphenyls [PCBs], detergents, fertilizers, inorganic chemicals (e.g, arsenic, cadmium, mercury, lead, nickel, phosphates, nitrates, fluorides, etc.) and radioactive wastes.
  • Biological water pollutants
    Biological water pollutants include pathogens such as bacteria, viruses, fungi, protozoa, helminthes, and nematodes.


Air movement in coastal areas: In coastal areas, at daytime, there is a regular flow of cool air from the sea towards the land, whereas at night, there is a reverse flow of air from land to sea.

  • The major cause of pollution of water is sewage, industrial wastes, pesticides and fertilizers from farming. Pollutants are leaked into underground water by garbage dumping.
  • The addition of undesirable substances to water-bodies:
    • Water containing soaps and detergents is discharged from houses and certain factories.
    • Effluents of mills and industries such as paper mills, petroleum refineries, etc, contain large quantities of harmful chemicals including acids, alkalis and heavy metals.
    • Animal excreta discharged into fields or dumped in to pits reaches water bodies through run off and leaching, particularly during the rainy season.
  • Thermal pollution:
    • Discharge of hot water from industries and thermal plants into water body changes the normal temperature of the water.
    • The removal of desirable substances from water-bodies causes harm to x the animals and plants that use dissolved oxygen in water.
  • A change in temperature:
    • Aquatic organisms are used to a certain range of temperature in the water-body where they live, and a sudden marked change in this temperature would be dangerous for them or affect their breeding.
    • The eggs and larvae of various animals are particularly susceptible to temperature changes.

Harmful effects of water pollution:

  • Human diseases:
    • The Pathogens which are biological pollutants of water cause human diseases such as typhoid, cholera, dysentery, jaundice, and hepatitis.
  • Disturbance in ecological balance:
    • The water pollutants affect the life forms in the water.
  • Removal of desirable substances from water bodies:
    • The increase in organic wastes, multiplies the bacteria.
    • The bacteria use up the oxygen.
    • This decreases the oxygen in the water body, in turn killing the fishes and other animals.
  • Effect of thermal pollution or change in temperature
    • Aquatic organisms are used to a certain range of temperature in the water-body where they live; a sudden marked change in this temperature can be dangerous for them.
  • Destruction of useful microorganisms
    • When untreated industrial wastes get mixed with water in rivers and lakes, etc.,  the acids, alkalies and heavy metals present in the industrial wastes kill the useful organisms present in water bodies.
  • Eutrophication:
    • Presence of sewage and fertilizers in polluted water provide a lot of nutrients to the algae (phytoplankton) present in water body, resulting excessive growth of algae.
    • The algae subsequently die and aerobic decomposers become active. They rapidly consume the dissolved oxygen of the water during decomposition of the dead algae.
  • Biomagnification (food chain magnification) of chemical
    • Pesticides such as DDT, DDE, dieldrin, etc., are harmful chemicals that are regularly being used in agriculture to protect crops from the pests.
    • These chemicals are non-biodegradable.
    • These pesticides/heavy metals enter the soil or are washed away by runoff water then enter the food chain via the producers.
    • At each trophic level, their concentration goes on increasing.
    • This phenomenon of increase in concentration of harmful non-biodegradable chemical substances in the body of living organisms at each trophic level of the food chain is called biomagnification.
    • Due to biomagnification fish-eating predatory birds such as kingfishers, osprey and loon become poisoned.
  • Decomposition of organic matter
    • Microorganisms bring about decomposition of organic matter brought about by sewage and other organic remains.
    • If organic matter is large or oxygen content is low, anaerobic breakdown of organic matter occurs.
    • This produces various pollutants such as hydrogen sulphides, ammonia, methyl sulphides.
    • The water of such a water body becomes odorous and turbid.

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