NCERT Textbook: Water- A Precious Resource | General Science(Prelims) by IRS Divey Sethi - UPSC PDF Download

 Page 1


Water: A Precious
Resource
16
You are perhaps aware that 22 March is
celebrated as the world water day! A
school celebrated ‘water day’ and invited
posters from the children of your age
group. Some of the posters presented
on that day are shown in Fig. 16.1.
“
Jal Hai, To Kal Hai
”
“If you have water, you can think of the future”
teachers must very often be advising you
not to waste water. No wonder we
celebrate water day every year to attract
the attention of everybody towards the
importance of conserving water.
The amount of water recommended
by the United Nations for drinking,
washing, cooking and maintaining proper
hygiene is a minimum of 50 litres per
person per day. This amount is about
two and a half buckets of water per
person per day. Is your family getting at
least this much of water? If yes, you
should consider yourself fortunate
because millions of people in our
country do not get enough water. What
about your friends and their families?
Share your experience with them.
In some places there is an acute
shortage of water. Taps running dry,
long queues for water (Fig. 16.2), fights,
marches and protests for demand of
water have become a common sight,
especially during summers. Some of the
newspaper clippings shown in Fig. 16.3
clearly indicate this message. Is it not
true that we face acute shortage of
water?
Fig. 16.1  Collage of posters
What is the message you get from
these posters? Write your observations
in your notebook and discuss them in
the class.
Have you ever felt a shortage of water
at home or at school? Your parents or
2022-23
Page 2


Water: A Precious
Resource
16
You are perhaps aware that 22 March is
celebrated as the world water day! A
school celebrated ‘water day’ and invited
posters from the children of your age
group. Some of the posters presented
on that day are shown in Fig. 16.1.
“
Jal Hai, To Kal Hai
”
“If you have water, you can think of the future”
teachers must very often be advising you
not to waste water. No wonder we
celebrate water day every year to attract
the attention of everybody towards the
importance of conserving water.
The amount of water recommended
by the United Nations for drinking,
washing, cooking and maintaining proper
hygiene is a minimum of 50 litres per
person per day. This amount is about
two and a half buckets of water per
person per day. Is your family getting at
least this much of water? If yes, you
should consider yourself fortunate
because millions of people in our
country do not get enough water. What
about your friends and their families?
Share your experience with them.
In some places there is an acute
shortage of water. Taps running dry,
long queues for water (Fig. 16.2), fights,
marches and protests for demand of
water have become a common sight,
especially during summers. Some of the
newspaper clippings shown in Fig. 16.3
clearly indicate this message. Is it not
true that we face acute shortage of
water?
Fig. 16.1  Collage of posters
What is the message you get from
these posters? Write your observations
in your notebook and discuss them in
the class.
Have you ever felt a shortage of water
at home or at school? Your parents or
2022-23
SCIENCE 194
Activity 16.1
Collect clippings from newspapers and
magazines on the news items, articles
and pictures related to water shortage.
Paste them in your scrapbook and share
it with your friends. List some problems
faced by the people and discuss them
in the class.
Water shortage has become a matter
of concern throughout the world. It is
estimated that in a few years from now
Fig. 16.4  Earth appears blue from space
Fig. 16.2  Long queue for water
Fig. 16.3  Newspaper clippings
Year 2003 was observed as
the International Year of
Freshwater to make people
aware of this dwindling natural resource.
more than one third of the people in
the world could face water scarcity.
Before we discuss why water is
getting scarce we must know how much
water is available for use on our planet.
16.1 HOW MUCH WATER IS
AVAILABLE
Look at the picture of the earth taken
from space. Why does it appear blue?
Surely, you can guess!
You are aware that about 71% of
the earth’s surface is covered with
water. Almost all the water on the
earth is contained in the seas and
oceans, rivers, lakes, ice caps, as
groundwater and in the atmosphere.
However, most of this water is not fit for
human consumption directly. The water
2022-23
Page 3


Water: A Precious
Resource
16
You are perhaps aware that 22 March is
celebrated as the world water day! A
school celebrated ‘water day’ and invited
posters from the children of your age
group. Some of the posters presented
on that day are shown in Fig. 16.1.
“
Jal Hai, To Kal Hai
”
“If you have water, you can think of the future”
teachers must very often be advising you
not to waste water. No wonder we
celebrate water day every year to attract
the attention of everybody towards the
importance of conserving water.
The amount of water recommended
by the United Nations for drinking,
washing, cooking and maintaining proper
hygiene is a minimum of 50 litres per
person per day. This amount is about
two and a half buckets of water per
person per day. Is your family getting at
least this much of water? If yes, you
should consider yourself fortunate
because millions of people in our
country do not get enough water. What
about your friends and their families?
Share your experience with them.
In some places there is an acute
shortage of water. Taps running dry,
long queues for water (Fig. 16.2), fights,
marches and protests for demand of
water have become a common sight,
especially during summers. Some of the
newspaper clippings shown in Fig. 16.3
clearly indicate this message. Is it not
true that we face acute shortage of
water?
Fig. 16.1  Collage of posters
What is the message you get from
these posters? Write your observations
in your notebook and discuss them in
the class.
Have you ever felt a shortage of water
at home or at school? Your parents or
2022-23
SCIENCE 194
Activity 16.1
Collect clippings from newspapers and
magazines on the news items, articles
and pictures related to water shortage.
Paste them in your scrapbook and share
it with your friends. List some problems
faced by the people and discuss them
in the class.
Water shortage has become a matter
of concern throughout the world. It is
estimated that in a few years from now
Fig. 16.4  Earth appears blue from space
Fig. 16.2  Long queue for water
Fig. 16.3  Newspaper clippings
Year 2003 was observed as
the International Year of
Freshwater to make people
aware of this dwindling natural resource.
more than one third of the people in
the world could face water scarcity.
Before we discuss why water is
getting scarce we must know how much
water is available for use on our planet.
16.1 HOW MUCH WATER IS
AVAILABLE
Look at the picture of the earth taken
from space. Why does it appear blue?
Surely, you can guess!
You are aware that about 71% of
the earth’s surface is covered with
water. Almost all the water on the
earth is contained in the seas and
oceans, rivers, lakes, ice caps, as
groundwater and in the atmosphere.
However, most of this water is not fit for
human consumption directly. The water
2022-23
WATER: A PRECIOUS RESOURCE 195
Paheli quickly calculated and
found that this amount is
roughly 0.006% of all water
found on the earth.
that is fit for use is freshwater. Perform
the following activity to estimate roughly
the relative amount of water available
in some of these sources.
Activity 16.2
Most of us assume water to be a limitless
resource. From this activity can you
Remark
Assume that this water
represents all the water present
on the earth.
This represents total
freshwater on the earth.
This gives a measure of usable
water present as ground-
water.
It represents all the water
present in all the lakes and
rivers of the world.
Steps
Take a medium-sized bucket
and fill it up with water. It
contains about twenty litres of
water. 
Take a tea spoon of about 5 mL
capacity and transfer 100
spoons of water from the bucket
to a small container, like a bath
mug.
From the bath mug transfer
thirty spoons of water to a glass
tumbler.
Finally take out a quarter (1/4
th
)
spoonfull of water from the mug.
Figure
n The water left in the bucket represents the saline water present in the seas,
oceans and partly as groundwater. This water is not fit for human use.
n The water left in the bath mug represents the water, which is present in the
frozen form in glaciers, ice caps and permanent snow; again not available readily.
Boojho wondered about the
alarmingly small quantity of
water available for our use.
2022-23
Page 4


Water: A Precious
Resource
16
You are perhaps aware that 22 March is
celebrated as the world water day! A
school celebrated ‘water day’ and invited
posters from the children of your age
group. Some of the posters presented
on that day are shown in Fig. 16.1.
“
Jal Hai, To Kal Hai
”
“If you have water, you can think of the future”
teachers must very often be advising you
not to waste water. No wonder we
celebrate water day every year to attract
the attention of everybody towards the
importance of conserving water.
The amount of water recommended
by the United Nations for drinking,
washing, cooking and maintaining proper
hygiene is a minimum of 50 litres per
person per day. This amount is about
two and a half buckets of water per
person per day. Is your family getting at
least this much of water? If yes, you
should consider yourself fortunate
because millions of people in our
country do not get enough water. What
about your friends and their families?
Share your experience with them.
In some places there is an acute
shortage of water. Taps running dry,
long queues for water (Fig. 16.2), fights,
marches and protests for demand of
water have become a common sight,
especially during summers. Some of the
newspaper clippings shown in Fig. 16.3
clearly indicate this message. Is it not
true that we face acute shortage of
water?
Fig. 16.1  Collage of posters
What is the message you get from
these posters? Write your observations
in your notebook and discuss them in
the class.
Have you ever felt a shortage of water
at home or at school? Your parents or
2022-23
SCIENCE 194
Activity 16.1
Collect clippings from newspapers and
magazines on the news items, articles
and pictures related to water shortage.
Paste them in your scrapbook and share
it with your friends. List some problems
faced by the people and discuss them
in the class.
Water shortage has become a matter
of concern throughout the world. It is
estimated that in a few years from now
Fig. 16.4  Earth appears blue from space
Fig. 16.2  Long queue for water
Fig. 16.3  Newspaper clippings
Year 2003 was observed as
the International Year of
Freshwater to make people
aware of this dwindling natural resource.
more than one third of the people in
the world could face water scarcity.
Before we discuss why water is
getting scarce we must know how much
water is available for use on our planet.
16.1 HOW MUCH WATER IS
AVAILABLE
Look at the picture of the earth taken
from space. Why does it appear blue?
Surely, you can guess!
You are aware that about 71% of
the earth’s surface is covered with
water. Almost all the water on the
earth is contained in the seas and
oceans, rivers, lakes, ice caps, as
groundwater and in the atmosphere.
However, most of this water is not fit for
human consumption directly. The water
2022-23
WATER: A PRECIOUS RESOURCE 195
Paheli quickly calculated and
found that this amount is
roughly 0.006% of all water
found on the earth.
that is fit for use is freshwater. Perform
the following activity to estimate roughly
the relative amount of water available
in some of these sources.
Activity 16.2
Most of us assume water to be a limitless
resource. From this activity can you
Remark
Assume that this water
represents all the water present
on the earth.
This represents total
freshwater on the earth.
This gives a measure of usable
water present as ground-
water.
It represents all the water
present in all the lakes and
rivers of the world.
Steps
Take a medium-sized bucket
and fill it up with water. It
contains about twenty litres of
water. 
Take a tea spoon of about 5 mL
capacity and transfer 100
spoons of water from the bucket
to a small container, like a bath
mug.
From the bath mug transfer
thirty spoons of water to a glass
tumbler.
Finally take out a quarter (1/4
th
)
spoonfull of water from the mug.
Figure
n The water left in the bucket represents the saline water present in the seas,
oceans and partly as groundwater. This water is not fit for human use.
n The water left in the bath mug represents the water, which is present in the
frozen form in glaciers, ice caps and permanent snow; again not available readily.
Boojho wondered about the
alarmingly small quantity of
water available for our use.
2022-23
SCIENCE 196
appreciate the actual amount of water
available for human use? Does the
finding worry you? Discuss this in your
class.
16.2 FORMS OF WATER
Are you afraid that continuous use will
some day exhaust all the water available
for use? You know that water on the
earth has been maintained for millions
of years by various processes which
make the water cycle. You have studied
the water cycle in Class VI. Write in your
own words what you know about the
water cycle.
You know that when water circulates
through the water cycle it can be found
in all the three forms, i.e., solid, liquid
and gas— at any given time somewhere
on the earth. The solid form, snow and
ice, is present as ice caps at the poles of
the earth, snow-covered mountains and
glaciers. Liquid water is present in
oceans, lakes, rivers, and even
underground. The gaseous form is the
water vapour present in the air around
us. The continuous cycling of water
among its three forms keeps the total
amount of water on the earth constant
even when the whole world is using it.
Does it give you any relief?
Can you recall the processes involved
in water cycle? The following activity will
help you.
Activity 16.3
Fig. 16.5 shows the processes involved
in the water cycle. They are labelled by
numbers. Match these numbers with
the processes given in the jumbled form.
Most towns and cities have water
supply system maintained by the civic
1. rudgon rawet
2. atooniaervp
3. acestoonnnid
4. duclos
5. tspratniaoinr
6. aitfinlronit
7. ntciepirtaipo
Fig. 16.5   Water cycle
3
2
5
6
1
7
4
2022-23
Page 5


Water: A Precious
Resource
16
You are perhaps aware that 22 March is
celebrated as the world water day! A
school celebrated ‘water day’ and invited
posters from the children of your age
group. Some of the posters presented
on that day are shown in Fig. 16.1.
“
Jal Hai, To Kal Hai
”
“If you have water, you can think of the future”
teachers must very often be advising you
not to waste water. No wonder we
celebrate water day every year to attract
the attention of everybody towards the
importance of conserving water.
The amount of water recommended
by the United Nations for drinking,
washing, cooking and maintaining proper
hygiene is a minimum of 50 litres per
person per day. This amount is about
two and a half buckets of water per
person per day. Is your family getting at
least this much of water? If yes, you
should consider yourself fortunate
because millions of people in our
country do not get enough water. What
about your friends and their families?
Share your experience with them.
In some places there is an acute
shortage of water. Taps running dry,
long queues for water (Fig. 16.2), fights,
marches and protests for demand of
water have become a common sight,
especially during summers. Some of the
newspaper clippings shown in Fig. 16.3
clearly indicate this message. Is it not
true that we face acute shortage of
water?
Fig. 16.1  Collage of posters
What is the message you get from
these posters? Write your observations
in your notebook and discuss them in
the class.
Have you ever felt a shortage of water
at home or at school? Your parents or
2022-23
SCIENCE 194
Activity 16.1
Collect clippings from newspapers and
magazines on the news items, articles
and pictures related to water shortage.
Paste them in your scrapbook and share
it with your friends. List some problems
faced by the people and discuss them
in the class.
Water shortage has become a matter
of concern throughout the world. It is
estimated that in a few years from now
Fig. 16.4  Earth appears blue from space
Fig. 16.2  Long queue for water
Fig. 16.3  Newspaper clippings
Year 2003 was observed as
the International Year of
Freshwater to make people
aware of this dwindling natural resource.
more than one third of the people in
the world could face water scarcity.
Before we discuss why water is
getting scarce we must know how much
water is available for use on our planet.
16.1 HOW MUCH WATER IS
AVAILABLE
Look at the picture of the earth taken
from space. Why does it appear blue?
Surely, you can guess!
You are aware that about 71% of
the earth’s surface is covered with
water. Almost all the water on the
earth is contained in the seas and
oceans, rivers, lakes, ice caps, as
groundwater and in the atmosphere.
However, most of this water is not fit for
human consumption directly. The water
2022-23
WATER: A PRECIOUS RESOURCE 195
Paheli quickly calculated and
found that this amount is
roughly 0.006% of all water
found on the earth.
that is fit for use is freshwater. Perform
the following activity to estimate roughly
the relative amount of water available
in some of these sources.
Activity 16.2
Most of us assume water to be a limitless
resource. From this activity can you
Remark
Assume that this water
represents all the water present
on the earth.
This represents total
freshwater on the earth.
This gives a measure of usable
water present as ground-
water.
It represents all the water
present in all the lakes and
rivers of the world.
Steps
Take a medium-sized bucket
and fill it up with water. It
contains about twenty litres of
water. 
Take a tea spoon of about 5 mL
capacity and transfer 100
spoons of water from the bucket
to a small container, like a bath
mug.
From the bath mug transfer
thirty spoons of water to a glass
tumbler.
Finally take out a quarter (1/4
th
)
spoonfull of water from the mug.
Figure
n The water left in the bucket represents the saline water present in the seas,
oceans and partly as groundwater. This water is not fit for human use.
n The water left in the bath mug represents the water, which is present in the
frozen form in glaciers, ice caps and permanent snow; again not available readily.
Boojho wondered about the
alarmingly small quantity of
water available for our use.
2022-23
SCIENCE 196
appreciate the actual amount of water
available for human use? Does the
finding worry you? Discuss this in your
class.
16.2 FORMS OF WATER
Are you afraid that continuous use will
some day exhaust all the water available
for use? You know that water on the
earth has been maintained for millions
of years by various processes which
make the water cycle. You have studied
the water cycle in Class VI. Write in your
own words what you know about the
water cycle.
You know that when water circulates
through the water cycle it can be found
in all the three forms, i.e., solid, liquid
and gas— at any given time somewhere
on the earth. The solid form, snow and
ice, is present as ice caps at the poles of
the earth, snow-covered mountains and
glaciers. Liquid water is present in
oceans, lakes, rivers, and even
underground. The gaseous form is the
water vapour present in the air around
us. The continuous cycling of water
among its three forms keeps the total
amount of water on the earth constant
even when the whole world is using it.
Does it give you any relief?
Can you recall the processes involved
in water cycle? The following activity will
help you.
Activity 16.3
Fig. 16.5 shows the processes involved
in the water cycle. They are labelled by
numbers. Match these numbers with
the processes given in the jumbled form.
Most towns and cities have water
supply system maintained by the civic
1. rudgon rawet
2. atooniaervp
3. acestoonnnid
4. duclos
5. tspratniaoinr
6. aitfinlronit
7. ntciepirtaipo
Fig. 16.5   Water cycle
3
2
5
6
1
7
4
2022-23
WATER: A PRECIOUS RESOURCE 197
bodies. The water is drawn from
nearby lakes, rivers, ponds or
wells. The water is supplied
through a network of pipes.
Many villages do not have such
a water supply system. There
people fetch water directly from
the sources. Often people and
even children have to walk
several kilometres to fetch water
(Fig. 16.6). The children suffer
a lot. They cannot attend
school regularly since they
spend hours in fetching water.
place to place, and it may even change
at a given place. The water table may be
at a depth of less than a metre or may
be several metres below the ground. The
water found below the water table is
called groundwater. What is the source
of this groundwater?
The rainwater and water from other
sources such as rivers and ponds seeps
through the soil and fills the empty
spaces and cracks deep below the
ground. The process of seeping of water
into the ground is called infiltration.
The groundwater thus gets recharged
by this process. At places the
groundwater is stored between layers of
hard rock below the water table. This is
known as an aquifer. Water in the
aquifers can be usually pumped out with
the help of tube wells or handpumps.
Have you ever been to a site where
construction work is going on? From
Women have to
perform a number of
household chores. If they have
also to spend time to fetch water
it adds to their burden.
A large number of people draw water
from wells, tube wells or hand pumps.
From where do these sources get water?
16.3 GROUNDWATER AS AN
IMPORTANT SOURCE OF WATER
If we dig a hole in the ground near a
water body we may find that the soil is
moist. The moisture in the soil indicates
the presence of water underground. If
we dig deeper and deeper, we would
reach a level where all the space between
particles of soil and gaps between rocks
are filled with water (Fig. 16.7). The
upper level of this layer is called the
water table. The water table varies from
Fig. 16.6  Women fetching water
2022-23