UNIT 2
Water
Learning Objectives
After completing this lesson, students
will be able to:
* know about the sources of water.
* understand the importance of water
management.
* get awareness on water pollution.
* know about waterborne diseases.
Introduction
நீர்இன்று அமையாது
உலகெனின்
யார்யார்க்கும்
வான்இன்று அமையாது
ஒழுக்கு.-
திருக்குறள்
Thirukkural says, ‘If it be said that
the duties of life cannot be discharged by any person without water, so without
rain there cannot be the flowing of water’. We can’t survive without water.
Water was once available in the nature freely. Now it is sold in the shops for
money. Water has become scarce nowadays. So, we should preserve it for our
basic needs and also for the needs of future generation. In this lesson we will
study about the sources of water, how to manage water, how it is polluted and
how the polluted water causes diseases.
I. Sources of Water
Water is the most abundant substance on
the Earth. It fills the seas, rivers and lakes, and covers more than two-thirds
of the earth’s surface. It also exists as snow and ice on mountains. In the
atmosphere, water is present in huge quantities as vapour and clouds. The
following are the sources of water.
1. River water and lake water
2. Sea water
3. Well water
4. Spring water
5. Underground water
1. River Water and Lake Water
River is a channel through which fresh
water flows. The origin of river is usually hills or mountains. It flows
towards ocean, sea and lakes. Lake is an area filled with water. Man-made lakes
created when dam is built on a river is called reservoir. Small areas filled
with water are called ponds. Rivers, streams, groundwater, rainfall, melting
snows or a combination of these are the sources of water in lakes, reservoirs
and ponds. As less amount of salt is dissolved in it, it is suitable for drinking
and irrigation.
2. Sea Water
Due to the presence of more amount of
salt, sea water is called saline water. It is not suitable for irrigation as
well as drinking. Sea water has salinity of approximately 3.5% or 35 parts per
thousand. This means that every 1000 ml of sea water contains 35 grams of salts
(Sodium chloride) dissolved in it.
3. Underground Water
During rainfall, part of the rain water gets absorbed in the soil. It flows through various layers of the soil till it reaches hard rock, where it gets accumulated to form reservoir. This reservoir of water is the underground water. This water may contain soluble salts of calcium and magnesium. Underground water is made available for human use either as well water or spring water
Do you know?
Underground water is free
from suspended impurities, because it is filtered by nature as it passes
through several layers of the soil.
4. Well Water
When the earth’s surface is dug deep,
water reservoirs are found above the rocks. The depth of a well varies from
place to place. Well water contains soluble impurities depending upon the
nature of soil.
5. Spring Water
Sometimes the accumulated underground
water applies pressure on the rocks and comes out of the earth’s surface in the
form of a spring from any available opening. This water is called spring water.
Spring water usually contains dissolved salts and minerals but it is free from
suspended impurities.
II. Water Cycle
Continuous movement of water from the
Earth to the atmosphere and back to the Earth is known as water cycle or
hydrologic cycle. Water cycle consists of the following four stages.
* Evaporation
The process in which water is changed
into water vapour by the heat of the sun is called evaporation. It takes place
from the surfaces of rivers, oceans, lakes and ponds. Plants also release water
by transpiration.
* Condensation
The process of converting water vapour
into water on cooling is called condensation. Water vapour in the atmosphere
being lighter, rises up and cools down. It further condenses to form tiny water
droplets.
* Precipitation
The
water droplets join together to form clouds. As they get cooler, the droplets
become bigger and heavier and fall as rain. If the air is very cold, they
freeze to fall as hail of snow.
* Flowing back to Oceans
Rain
water forms streams and springs which join together to form rivers. Rivers flow
finally into the sea and ocean thereby completing the cycle.
Do you know?
In freezing conditions,
water falling from the sky becomes snow or hail. Hail stones are balls of ice.
Activity 1
Take half a glass of
water. Clean the outside part of the glass. Add few ice cubes and leave it for
5-10 minutes. You will observe drops of water appearing outside the glass. This
happens because the water vapour in the air condenses on the cold surface of
the glass.
III. Water Management
About 97% of total water available on
the earth is too salty to be used for drinking and irrigation. The rest 3% of
water is fresh water. Most of the fresh water i.e., 68.7% of the total fresh
water is frozen as ice caps and glaciers and 30.1% occurs as ground water. Out
of the remaining 1.2% of water, about 0.9% occurs as moisture in soil, air and
in bodies of living organisms. The rest 0.3% constitutes fresh surface water
sources, such as rivers and lakes. It amounts to about 700th part of one
percent (1/700) of total water available on earth. By this it is clear that a
very small fraction of water is available for the use of human beings, animals
and plants. The following figure shows the percentage distribution of total
available water.
Do you know?
Agriculture is the source
of our living. It uses most of the world’s fresh water resources. It consumes
around 70% of the available fresh water.
1. Fresh Water Management
Water management is the activity of
planning, developing and managing the optimum use of water resources. Water
which is obtained naturally from ice sheets, ice caps, glaciers, ice bergs,
ponds, lakes, rivers, streams and underground are called fresh water. Fresh
water is having low concentrations of dissolved salts. Nowadays we don’t get
enough rainfall and except few, most of the rivers are drained. Due to recent
changes in the climate we don’t have water in lakes and ponds. People in many
countries suffer without water even for their basic needs. So, we need to
manage the available water.
* Rain Water Harvesting
The process of collecting rain water
from the roof top of the buildings is called rain water harvesting. In this
system rain water is stored into a storage tank for later use. Rain water
available in the open spaces around the buildings may also be recharged into
the ground. It is another method of rainwater harvesting. The government of
Tamil Nadu leads the nation in implementing rain water harvesting programme. It
has made it mandatory for all houses and buildings in the state to install rain
water harvesting facility.
Advantages
→ Rain
water harvesting can reduce flooding in the cities.
→ Rain
water harvesting can reduce top soil loss.
→ Ground
water level can be increased.
→ Ground
water can be conserved.
→ It
can improve plant growth.
Do
you know?
March 22 is observed as
World Water Day.
Activity 2
Estimate the amount of
water used by your family in a day for drinking, brushing, bathing, cleaning
vessels, washing cloths, toilets and cleaning the floor. Find out for which
activity water usage is more and how it can be minimized.
* Farm Ponds
A farm pond is a structure dug out on
the Earth. It is usually square or rectangular in shape. Rainwater is stored in
it for irrigation purposes. It is surrounded by a small bund, which prevents
erosion on the banks of the pond. The size and depth of the pond depend on the
type of the soil, water requirements of the farmer, its uses and the cost of
excavation. Water is conveyed to the fields manually, by pumping, or by both.
2. Waste Water Management
Used water from any combination of
activities such as domestic (houses), industrial, commercial, agricultural is
called waste water. This water has been used for laundry, bathing, dish
washing, toilets and industrial purposes. Waste water also includes rain water
that has been accumulated pollutants as it runs into the oceans, lakes and
rivers. Pollutants are unwanted chemicals or materials that contaminate water.
The goal of waste water management is to clean and protect water so that it can
be reused. It also must be clean before it flows into oceans, lakes and rivers.
* Waste Water Treatment
Generally, waste water is treated by
physical, chemical and biological processes using filtration, sedimentation,
adding cow dung, powder and bacteria. This method is followed in industries.
Activity 3
Visit an industry in your area with the help of your teacher. Observe and note the waste water treatment process.
Advantages
→ Waste water treatment
ensures that the environment is clean.
→ There is no water
pollution.
→ It prevents waterborne
diseases.
→ It ensures that there is
adequate water for irrigation.
3. Desalination of
Sea Water
Desalination is an artificial process of
converting saline water (sea water) into fresh water. The common desalination
processes are:
* Distillation
*Reverse Osmosis
The process in which both evaporation
and condensation go side by side is called distillation. Reverse osmosis is a
process of forcing water under pressure through a semi permeable membrane. Tiny
pores in the membrane allow water to pass but exclude most salts and minerals.
The reverse osmosis process helps to solve the water scarcity problem.
IV. Water Pollution
Contamination of water bodies by human
activities is called water pollution. Our water resources (pond, lake, river,
canal and well) are polluted by sanitary water,
industrial wastes, insecticides, fertilizers, sewages, synthetic detergents, chemical
fertilizers, oil, heavy metals and radioactive wastes. These unwanted and
harmful substances which pollute water are called water pollutants.
1. Sources of Water Pollution
The major sources of water pollution are
industrial waste, sewage, domestic waste, chemical fertilizers and
insecticides, synthetic detergents and oil spill.
Do you know?
25% of the world
population does not get safe drinking water.
* Industrial Waste
The discharge of untreated industrial
wastes from the industries into rivers and lakes is one of the main causes of
water pollution. The industrial wastes contain harmful substances such as acid,
alkalis and hot water. The chemicals like Arsenic, Lead, Mercury and Cadmium
are released by the industries and it leads to toxicity in plants and animals.
* Sewage
The dumping of sewage into rivers and
lakes is the second major cause of water pollution in big cities.
* Domestic Waste
Food waste, soaps and detergents,
garbage, wrappers, plastics and other materials carried by the flowing water
pollute the water bodies.
* Chemical Fertilizers and Insecticides
The excess use of fertilizers and
pesticides causes water pollution. Because these chemicals are washed into the
rivers and lakes with rainwater, they pollute the soil and underground water
also. Pesticides like DDT (Dichloro Diphenyl Trichloroethane) enter the bodies
of aquatic animals and reach the human body by way of food chain.
* Synthetic Detergents
Excess use of synthetic detergents for
washing purposes produces foam and they pollute the water.
* Oil Spill
Oil leakages on the surface of the sea
affect the marine organisms.
2. Prevention of Water Pollution
* Excess use of fertilizers and
pesticides should be avoided in agricultural land.
* Use of synthetic detergents should be
minimized or biodegradable detergents should be used.
* Trees and shrubs should be planted
along the banks of the rivers or lakes.
* Plastic waste, food materials and
vegetables should not be thrown into open drains.
* Proper sewage treatment and management
should be implemented.
V. Waterborne Diseases
Illness caused by the micro-organisms
present in the untreated or contaminated water is called waterborne diseases. They
are responsible for morbidity and mortality in all age groups particularly
among children under 5 years of age. It is believed that 80% of all diseases in
the world are caused by inadequate sanitation and polluted water. Poverty,
illiteracy, overcrowding and low health services are also directly or
indirectly responsible for the prevalence of these diseases.
1. Types of Waterborne Diseases
Diarrhoea, dysentery, typhoid and
cholera are some of the common waterborne diseases. They are caused by
micro-organisms like bacteria and virus. Some of them are spread by mosquitoes.
The following table gives the causative agents and the symptoms of few waterborne
diseases.
Do you know?
People all over the world
are worstly affected by diarrhoeal diseases. Three million people die worldwide
every year due to these diseases.
Activity 4
Visit a primary health
centre in your area and find out the common waterborne diseases prevalent among
the people. Also find out the causes for them.
2. Prevention of Waterborne Diseases
* Good personal hygiene should be
practiced and basic sanitation should be improved.
* Chlorinated and boiled water should be
used for drinking.
* Drink boiled or pasteurized milk.
* Dispose infectious wastes properly.
VI. Other Diseases
Apart from the waterborne diseases
mentioned above, there are many diseases which are spread by vectors which
breed in stagnant water in our surrounding. For example, Aedes mosquito breeds
in stagnant water and it causes Dengue fever. Similarly, pigs feed in the
stagnant sewage water. The pigs infected by virus spread Swine flu.
1. Dengue Fever
Dengue is a viral disease spread by
Aedes female mosquitoes that bite during day time. They breed in clean stagnant
water found in containers and old tyres.
Symptoms
* Symptoms may include high fever,
severe head ache, muscle and joint pain and a characteristic skin rash.
* Symptoms of Dengue fever typically
begin three to fourteen days after infection.
* Deficiency of platelets in blood.
* Intense stomach pain.
* Regular vomiting with blood.
Prevention
* Spray the house with anti mosquito
spray.
* Try to wear cloths that cover skin
areas.
* Close the doors and windows during
early morning and evening.
* Do not leave stagnant water anywhere
in and around the house.
Do you know?
Aedes mosquitoes also
transmit Chikungunya and Yellow fever. This can result in death if any treatment
is not taken.
Treatment
* Dengue is caused by a virus and so
there is no specific treatment or cure.
* A high fever and vomiting can
dehydrate the body. So the person should drink clean water (bottle water).
* Rehydration salts can help replace the
fluids and minerals lost in the body.
* Taking pain killers like Tylenol or
Paracetamol can help to reduce fever and ease pain.
2. Swine Flu (H1N1)
Swine flu is a respiratory disease
caused by Influenza virus that infects the respiratory tracts of pigs and results
in barking cough. It can be transmitted to human beings. People who are
constantly exposed to pigs are at risk of Swine flu infection. By keeping our
surrounding free from sewage water, we can avoid exposure to pigs.
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