NCERT Textbook: Water | Science & Technology for UPSC CSE PDF Download

 Page 1


136 SCIENCE
14
Water
S
uppose for some reason your
family gets only one bucket of
water everyday for a week.
Imagine what would happen? Would you
be able to cook, clean utensils, wash
clothes or bathe? What are the other
activities you would not be able to do?
What would happen if we do not have
easy access to water for a long period
of time?
Apart from drinking, there are
so many activities for which we use
water (Fig. 14.1). Do you have an idea
about the quantity of water we use in a
single day?
each activity by you and other family
members. You may use a mug, a glass,
a bucket or any other container to
measure the amount of water used.
Fig. 14.1 Uses of water
14.1 HOW MUCH WATER DO WE USE?
Activity 1
List all the activities for which you use
water in a day. Some activities are listed
in Table 14.1. Make a similar table in
your notebook. Throughout the day,
measure the amount of water used for
Table 14.1  Estimation of the
amount of water used by your
family in a day
y t i v i t c A
f o t n u o m A
d e s u r e t a w
g n i k n i r D
g n i h s u r B
g n i h t a B
s l i s n e t u g n i h s a W
s e h t o l c g n i h s a W
s t e l i o T
r o o l f g n i n a e l C
r e h t o y n A
n i d e s u r e t a w l a t o T
y l i m a f a y b y a d a
You now have a rough idea as to how
much water your family uses in a day.
Can you estimate the amount of water
used by you for personal cleanliness in
a day. Using this information, calculate
the amount of water needed by your
family in a year. Now, divide this amount
by the number of members of your
family. This will give an idea of the
amount of water needed by one member
of your family in a year. Find the number
of people that live in your village or town.
2022-23
Page 2


136 SCIENCE
14
Water
S
uppose for some reason your
family gets only one bucket of
water everyday for a week.
Imagine what would happen? Would you
be able to cook, clean utensils, wash
clothes or bathe? What are the other
activities you would not be able to do?
What would happen if we do not have
easy access to water for a long period
of time?
Apart from drinking, there are
so many activities for which we use
water (Fig. 14.1). Do you have an idea
about the quantity of water we use in a
single day?
each activity by you and other family
members. You may use a mug, a glass,
a bucket or any other container to
measure the amount of water used.
Fig. 14.1 Uses of water
14.1 HOW MUCH WATER DO WE USE?
Activity 1
List all the activities for which you use
water in a day. Some activities are listed
in Table 14.1. Make a similar table in
your notebook. Throughout the day,
measure the amount of water used for
Table 14.1  Estimation of the
amount of water used by your
family in a day
y t i v i t c A
f o t n u o m A
d e s u r e t a w
g n i k n i r D
g n i h s u r B
g n i h t a B
s l i s n e t u g n i h s a W
s e h t o l c g n i h s a W
s t e l i o T
r o o l f g n i n a e l C
r e h t o y n A
n i d e s u r e t a w l a t o T
y l i m a f a y b y a d a
You now have a rough idea as to how
much water your family uses in a day.
Can you estimate the amount of water
used by you for personal cleanliness in
a day. Using this information, calculate
the amount of water needed by your
family in a year. Now, divide this amount
by the number of members of your
family. This will give an idea of the
amount of water needed by one member
of your family in a year. Find the number
of people that live in your village or town.
2022-23
137 WATER
You have listed a number of activities
for which you use water. Do you think,
our water requirement is limited to
activities like these? We use wheat, rice,
pulses, vegetables and many other food
items everyday. We know that some of
the fibres that we use for making fabric
come from plants. Is water not needed
to grow these? Can you think of some
more uses of water? Water is used in
industries for producing almost all the
things that we use. So, we need water
not only for our daily activities but also
for producing many things.
water from a river, spring, pond, well or
a hand pump”. Some others might say,
“We get water from taps”. Have you ever
wondered where water in the taps comes
from? Water that we get from taps is also
drawn from a lake or a river or a well
(Fig. 14.2). It is then supplied through
a network of pipes.
Fig. 14.2 Water in taps comes from rivers,
lakes, borewell or wells
Boojho wonders whether people
living in different regions of our
country get the same amount of
water. Are there regions where
people do not get adequate amount
of water? How do they manage?
You may now get an idea of the amount
of water needed by your village or town
in a year.
Paheli wants to tell you that
about two glasses of water
are required to produce
each page of a book.
Each of us may be getting water into
our homes in different ways. But, finally,
all of us get water from the same sources
such as ponds, lakes, rivers and wells.
We have discussed some of the
sources of water. Where does the water
come from, to fill these ponds, lakes,
rivers and wells?
Boojho wants you to imagine a
day in your life when water supply
through taps is not available. So,
you have to fetch it yourself from
a far away place. Would you
use the same amount of water
as on any other day?
14.2 WHERE DO WE GET WATER
FROM?
Where do you get the water that you
use? Some of you may say, “We draw
2022-23
Page 3


136 SCIENCE
14
Water
S
uppose for some reason your
family gets only one bucket of
water everyday for a week.
Imagine what would happen? Would you
be able to cook, clean utensils, wash
clothes or bathe? What are the other
activities you would not be able to do?
What would happen if we do not have
easy access to water for a long period
of time?
Apart from drinking, there are
so many activities for which we use
water (Fig. 14.1). Do you have an idea
about the quantity of water we use in a
single day?
each activity by you and other family
members. You may use a mug, a glass,
a bucket or any other container to
measure the amount of water used.
Fig. 14.1 Uses of water
14.1 HOW MUCH WATER DO WE USE?
Activity 1
List all the activities for which you use
water in a day. Some activities are listed
in Table 14.1. Make a similar table in
your notebook. Throughout the day,
measure the amount of water used for
Table 14.1  Estimation of the
amount of water used by your
family in a day
y t i v i t c A
f o t n u o m A
d e s u r e t a w
g n i k n i r D
g n i h s u r B
g n i h t a B
s l i s n e t u g n i h s a W
s e h t o l c g n i h s a W
s t e l i o T
r o o l f g n i n a e l C
r e h t o y n A
n i d e s u r e t a w l a t o T
y l i m a f a y b y a d a
You now have a rough idea as to how
much water your family uses in a day.
Can you estimate the amount of water
used by you for personal cleanliness in
a day. Using this information, calculate
the amount of water needed by your
family in a year. Now, divide this amount
by the number of members of your
family. This will give an idea of the
amount of water needed by one member
of your family in a year. Find the number
of people that live in your village or town.
2022-23
137 WATER
You have listed a number of activities
for which you use water. Do you think,
our water requirement is limited to
activities like these? We use wheat, rice,
pulses, vegetables and many other food
items everyday. We know that some of
the fibres that we use for making fabric
come from plants. Is water not needed
to grow these? Can you think of some
more uses of water? Water is used in
industries for producing almost all the
things that we use. So, we need water
not only for our daily activities but also
for producing many things.
water from a river, spring, pond, well or
a hand pump”. Some others might say,
“We get water from taps”. Have you ever
wondered where water in the taps comes
from? Water that we get from taps is also
drawn from a lake or a river or a well
(Fig. 14.2). It is then supplied through
a network of pipes.
Fig. 14.2 Water in taps comes from rivers,
lakes, borewell or wells
Boojho wonders whether people
living in different regions of our
country get the same amount of
water. Are there regions where
people do not get adequate amount
of water? How do they manage?
You may now get an idea of the amount
of water needed by your village or town
in a year.
Paheli wants to tell you that
about two glasses of water
are required to produce
each page of a book.
Each of us may be getting water into
our homes in different ways. But, finally,
all of us get water from the same sources
such as ponds, lakes, rivers and wells.
We have discussed some of the
sources of water. Where does the water
come from, to fill these ponds, lakes,
rivers and wells?
Boojho wants you to imagine a
day in your life when water supply
through taps is not available. So,
you have to fetch it yourself from
a far away place. Would you
use the same amount of water
as on any other day?
14.2 WHERE DO WE GET WATER
FROM?
Where do you get the water that you
use? Some of you may say, “We draw
2022-23
138 SCIENCE
Do you know that about two thirds
of the Earth is covered with water? Most
of this water is in oceans and seas
(Fig. 14.3).
The water in the oceans and seas has
many salts dissolved in it — the water
is saline. So, it is not fit for drinking
and other domestic, agricultural and
industrial needs. You might have heard
the famous lines of the poem “Rime of
the Ancient Mariner” written by S.T.
Coleridge in 1798:
“Water water every where
Nor any drop to drink”
Here the poet has described the
plight of sailors on a ship lost in the
ocean.
Yet, oceans play an important role
in supplying the water that we use. Do
you find this surprising? After all, the
water that we use is not salty. Many of
us live in places far away from the
oceans. Does the water supply in these
places also depend on the oceans? How
does the ocean water reach ponds, lakes,
rivers and wells, which supply us water?
How come  the water from these sources
is not saline anymore?
Do you remember Activity 6 in
Chapter 5 in which water with salt
dissolved in it was heated? What did we
find? The water evaporated and the salt
was left behind. This activity gives us
an idea that, on heating, water changes
into its vapour. We also realise from this
activity, that water vapour does not carry
away the salt with it. Water vapours so
formed become a part of the air and
cannot usually be seen. We also found
that heating is essential to convert water
into its vapour. However, we have seen
that water changes into its vapour also
Fig. 14.3  Oceans cover a major part of the earth
Fig. 14.4 Clothes drying on a clothes-line
That is where the water cycle
comes in!
14.3 WATER CYCLE
Disappearing Trick of Water
How many times have you noticed that
water spilled on a floor dries up after
some time? The water seems to disappear.
Similarly, water disappears from wet
clothes as they dry up (Fig. 14.4). Water
from wet roads, rooftops and a few other
places also disappears after the rains.
Where does this water go?
2022-23
Page 4


136 SCIENCE
14
Water
S
uppose for some reason your
family gets only one bucket of
water everyday for a week.
Imagine what would happen? Would you
be able to cook, clean utensils, wash
clothes or bathe? What are the other
activities you would not be able to do?
What would happen if we do not have
easy access to water for a long period
of time?
Apart from drinking, there are
so many activities for which we use
water (Fig. 14.1). Do you have an idea
about the quantity of water we use in a
single day?
each activity by you and other family
members. You may use a mug, a glass,
a bucket or any other container to
measure the amount of water used.
Fig. 14.1 Uses of water
14.1 HOW MUCH WATER DO WE USE?
Activity 1
List all the activities for which you use
water in a day. Some activities are listed
in Table 14.1. Make a similar table in
your notebook. Throughout the day,
measure the amount of water used for
Table 14.1  Estimation of the
amount of water used by your
family in a day
y t i v i t c A
f o t n u o m A
d e s u r e t a w
g n i k n i r D
g n i h s u r B
g n i h t a B
s l i s n e t u g n i h s a W
s e h t o l c g n i h s a W
s t e l i o T
r o o l f g n i n a e l C
r e h t o y n A
n i d e s u r e t a w l a t o T
y l i m a f a y b y a d a
You now have a rough idea as to how
much water your family uses in a day.
Can you estimate the amount of water
used by you for personal cleanliness in
a day. Using this information, calculate
the amount of water needed by your
family in a year. Now, divide this amount
by the number of members of your
family. This will give an idea of the
amount of water needed by one member
of your family in a year. Find the number
of people that live in your village or town.
2022-23
137 WATER
You have listed a number of activities
for which you use water. Do you think,
our water requirement is limited to
activities like these? We use wheat, rice,
pulses, vegetables and many other food
items everyday. We know that some of
the fibres that we use for making fabric
come from plants. Is water not needed
to grow these? Can you think of some
more uses of water? Water is used in
industries for producing almost all the
things that we use. So, we need water
not only for our daily activities but also
for producing many things.
water from a river, spring, pond, well or
a hand pump”. Some others might say,
“We get water from taps”. Have you ever
wondered where water in the taps comes
from? Water that we get from taps is also
drawn from a lake or a river or a well
(Fig. 14.2). It is then supplied through
a network of pipes.
Fig. 14.2 Water in taps comes from rivers,
lakes, borewell or wells
Boojho wonders whether people
living in different regions of our
country get the same amount of
water. Are there regions where
people do not get adequate amount
of water? How do they manage?
You may now get an idea of the amount
of water needed by your village or town
in a year.
Paheli wants to tell you that
about two glasses of water
are required to produce
each page of a book.
Each of us may be getting water into
our homes in different ways. But, finally,
all of us get water from the same sources
such as ponds, lakes, rivers and wells.
We have discussed some of the
sources of water. Where does the water
come from, to fill these ponds, lakes,
rivers and wells?
Boojho wants you to imagine a
day in your life when water supply
through taps is not available. So,
you have to fetch it yourself from
a far away place. Would you
use the same amount of water
as on any other day?
14.2 WHERE DO WE GET WATER
FROM?
Where do you get the water that you
use? Some of you may say, “We draw
2022-23
138 SCIENCE
Do you know that about two thirds
of the Earth is covered with water? Most
of this water is in oceans and seas
(Fig. 14.3).
The water in the oceans and seas has
many salts dissolved in it — the water
is saline. So, it is not fit for drinking
and other domestic, agricultural and
industrial needs. You might have heard
the famous lines of the poem “Rime of
the Ancient Mariner” written by S.T.
Coleridge in 1798:
“Water water every where
Nor any drop to drink”
Here the poet has described the
plight of sailors on a ship lost in the
ocean.
Yet, oceans play an important role
in supplying the water that we use. Do
you find this surprising? After all, the
water that we use is not salty. Many of
us live in places far away from the
oceans. Does the water supply in these
places also depend on the oceans? How
does the ocean water reach ponds, lakes,
rivers and wells, which supply us water?
How come  the water from these sources
is not saline anymore?
Do you remember Activity 6 in
Chapter 5 in which water with salt
dissolved in it was heated? What did we
find? The water evaporated and the salt
was left behind. This activity gives us
an idea that, on heating, water changes
into its vapour. We also realise from this
activity, that water vapour does not carry
away the salt with it. Water vapours so
formed become a part of the air and
cannot usually be seen. We also found
that heating is essential to convert water
into its vapour. However, we have seen
that water changes into its vapour also
Fig. 14.3  Oceans cover a major part of the earth
Fig. 14.4 Clothes drying on a clothes-line
That is where the water cycle
comes in!
14.3 WATER CYCLE
Disappearing Trick of Water
How many times have you noticed that
water spilled on a floor dries up after
some time? The water seems to disappear.
Similarly, water disappears from wet
clothes as they dry up (Fig. 14.4). Water
from wet roads, rooftops and a few other
places also disappears after the rains.
Where does this water go?
2022-23
139 WATER
from the fields, roads, rooftops and
other land areas. We also discussed in
Chapter 5 that to obtain salt, water from
the sea is left in shallow pits to let the
water evaporate. From where does this
water get the heat it needs to evaporate?
Let us find out.
Activity 2
Take two similar plates. Place one of the
plates in sunlight and keep the other
under shade. Now, pour equal amount
of water in each of the plates (Fig. 14.5).
You can use a cap of a bottle to measure
water. Make sure that water does not
spill over. Observe the two plates after
every 15 minutes. Does the water seem
to disappear? From which plate does it
disappear first? What is the source of
heat for this evaporation?
During the daytime, sunlight falls on
the water in oceans, rivers, lakes and
ponds. The fields and other land areas
also receive sunlight. As a result, water
from all these places continuously
changes into vapour. However, the salts
dissolved in the water are left behind.
In Activity 2, did you find that water
also disappeared from the plate kept in
the shade, though it could have taken
more time? Does the heat from the
sunlight reach here? Yes, during the
daytime all the air surrounding us gets
heated. This warm air provides heat for
evaporation of water in the shade. Thus,
evaporation takes place from all open
surfaces of water. As a result, water
vapour gets continuously added to air.
However, evaporation of water is a slow
process. That is why we rarely notice its
loss from a bucket full of water. In
sunlight, evaporation takes place faster.
On heating water on a burner, its
evaporation takes place even faster. Is
there any other process through which
water vapour gets transferred into air?
Loss of Water by Plants
You have learnt in Chapter 7 that plants
need water to grow. Plants use a part of
this water to prepare their food and
Fig.14.5 Evaporation of water in sunlight and in
shade
Boojho has been reading about
transpiration. He asked himself -
how much water is lost through
transpiration by wheat plants
that give us one kilogram of
wheat? He found out that this is
nearly 500 litres, that is, roughly
25 large sized buckets full of
water. Can you now imagine the
amount of water lost by plants
of all the forests, crops and
grasslands together?
2022-23
Page 5


136 SCIENCE
14
Water
S
uppose for some reason your
family gets only one bucket of
water everyday for a week.
Imagine what would happen? Would you
be able to cook, clean utensils, wash
clothes or bathe? What are the other
activities you would not be able to do?
What would happen if we do not have
easy access to water for a long period
of time?
Apart from drinking, there are
so many activities for which we use
water (Fig. 14.1). Do you have an idea
about the quantity of water we use in a
single day?
each activity by you and other family
members. You may use a mug, a glass,
a bucket or any other container to
measure the amount of water used.
Fig. 14.1 Uses of water
14.1 HOW MUCH WATER DO WE USE?
Activity 1
List all the activities for which you use
water in a day. Some activities are listed
in Table 14.1. Make a similar table in
your notebook. Throughout the day,
measure the amount of water used for
Table 14.1  Estimation of the
amount of water used by your
family in a day
y t i v i t c A
f o t n u o m A
d e s u r e t a w
g n i k n i r D
g n i h s u r B
g n i h t a B
s l i s n e t u g n i h s a W
s e h t o l c g n i h s a W
s t e l i o T
r o o l f g n i n a e l C
r e h t o y n A
n i d e s u r e t a w l a t o T
y l i m a f a y b y a d a
You now have a rough idea as to how
much water your family uses in a day.
Can you estimate the amount of water
used by you for personal cleanliness in
a day. Using this information, calculate
the amount of water needed by your
family in a year. Now, divide this amount
by the number of members of your
family. This will give an idea of the
amount of water needed by one member
of your family in a year. Find the number
of people that live in your village or town.
2022-23
137 WATER
You have listed a number of activities
for which you use water. Do you think,
our water requirement is limited to
activities like these? We use wheat, rice,
pulses, vegetables and many other food
items everyday. We know that some of
the fibres that we use for making fabric
come from plants. Is water not needed
to grow these? Can you think of some
more uses of water? Water is used in
industries for producing almost all the
things that we use. So, we need water
not only for our daily activities but also
for producing many things.
water from a river, spring, pond, well or
a hand pump”. Some others might say,
“We get water from taps”. Have you ever
wondered where water in the taps comes
from? Water that we get from taps is also
drawn from a lake or a river or a well
(Fig. 14.2). It is then supplied through
a network of pipes.
Fig. 14.2 Water in taps comes from rivers,
lakes, borewell or wells
Boojho wonders whether people
living in different regions of our
country get the same amount of
water. Are there regions where
people do not get adequate amount
of water? How do they manage?
You may now get an idea of the amount
of water needed by your village or town
in a year.
Paheli wants to tell you that
about two glasses of water
are required to produce
each page of a book.
Each of us may be getting water into
our homes in different ways. But, finally,
all of us get water from the same sources
such as ponds, lakes, rivers and wells.
We have discussed some of the
sources of water. Where does the water
come from, to fill these ponds, lakes,
rivers and wells?
Boojho wants you to imagine a
day in your life when water supply
through taps is not available. So,
you have to fetch it yourself from
a far away place. Would you
use the same amount of water
as on any other day?
14.2 WHERE DO WE GET WATER
FROM?
Where do you get the water that you
use? Some of you may say, “We draw
2022-23
138 SCIENCE
Do you know that about two thirds
of the Earth is covered with water? Most
of this water is in oceans and seas
(Fig. 14.3).
The water in the oceans and seas has
many salts dissolved in it — the water
is saline. So, it is not fit for drinking
and other domestic, agricultural and
industrial needs. You might have heard
the famous lines of the poem “Rime of
the Ancient Mariner” written by S.T.
Coleridge in 1798:
“Water water every where
Nor any drop to drink”
Here the poet has described the
plight of sailors on a ship lost in the
ocean.
Yet, oceans play an important role
in supplying the water that we use. Do
you find this surprising? After all, the
water that we use is not salty. Many of
us live in places far away from the
oceans. Does the water supply in these
places also depend on the oceans? How
does the ocean water reach ponds, lakes,
rivers and wells, which supply us water?
How come  the water from these sources
is not saline anymore?
Do you remember Activity 6 in
Chapter 5 in which water with salt
dissolved in it was heated? What did we
find? The water evaporated and the salt
was left behind. This activity gives us
an idea that, on heating, water changes
into its vapour. We also realise from this
activity, that water vapour does not carry
away the salt with it. Water vapours so
formed become a part of the air and
cannot usually be seen. We also found
that heating is essential to convert water
into its vapour. However, we have seen
that water changes into its vapour also
Fig. 14.3  Oceans cover a major part of the earth
Fig. 14.4 Clothes drying on a clothes-line
That is where the water cycle
comes in!
14.3 WATER CYCLE
Disappearing Trick of Water
How many times have you noticed that
water spilled on a floor dries up after
some time? The water seems to disappear.
Similarly, water disappears from wet
clothes as they dry up (Fig. 14.4). Water
from wet roads, rooftops and a few other
places also disappears after the rains.
Where does this water go?
2022-23
139 WATER
from the fields, roads, rooftops and
other land areas. We also discussed in
Chapter 5 that to obtain salt, water from
the sea is left in shallow pits to let the
water evaporate. From where does this
water get the heat it needs to evaporate?
Let us find out.
Activity 2
Take two similar plates. Place one of the
plates in sunlight and keep the other
under shade. Now, pour equal amount
of water in each of the plates (Fig. 14.5).
You can use a cap of a bottle to measure
water. Make sure that water does not
spill over. Observe the two plates after
every 15 minutes. Does the water seem
to disappear? From which plate does it
disappear first? What is the source of
heat for this evaporation?
During the daytime, sunlight falls on
the water in oceans, rivers, lakes and
ponds. The fields and other land areas
also receive sunlight. As a result, water
from all these places continuously
changes into vapour. However, the salts
dissolved in the water are left behind.
In Activity 2, did you find that water
also disappeared from the plate kept in
the shade, though it could have taken
more time? Does the heat from the
sunlight reach here? Yes, during the
daytime all the air surrounding us gets
heated. This warm air provides heat for
evaporation of water in the shade. Thus,
evaporation takes place from all open
surfaces of water. As a result, water
vapour gets continuously added to air.
However, evaporation of water is a slow
process. That is why we rarely notice its
loss from a bucket full of water. In
sunlight, evaporation takes place faster.
On heating water on a burner, its
evaporation takes place even faster. Is
there any other process through which
water vapour gets transferred into air?
Loss of Water by Plants
You have learnt in Chapter 7 that plants
need water to grow. Plants use a part of
this water to prepare their food and
Fig.14.5 Evaporation of water in sunlight and in
shade
Boojho has been reading about
transpiration. He asked himself -
how much water is lost through
transpiration by wheat plants
that give us one kilogram of
wheat? He found out that this is
nearly 500 litres, that is, roughly
25 large sized buckets full of
water. Can you now imagine the
amount of water lost by plants
of all the forests, crops and
grasslands together?
2022-23
140 SCIENCE
retain some of it in their different parts.
Remaining part of this water is released
by the plants into air, as water vapour
through the process of transpiration. Do
you remember observing transpiration
of water by plants in Activity 4 in
Chapter 7?
Water vapour enters the air through
the processes of evaporation and
transpiration. Is it lost for ever? No, we
get it back again, as we will see.
How are clouds formed?
Activity 3
Take a glass half filled with water. Wipe
the glass from the outside with a clean
piece of cloth. Add some ice into the
water. Wait for one or two minutes.
Observe the changes that take place on
the outer surface of the glass (Fig.14.6).
From where do water drops appear
on the outer side of the glass? The cold
surface of the glass containing iced water,
cools the air around it, and the water
vapour of the air condenses on the
surface of the glass. We noticed this
process of condensation in Activity 7 in
Chapter 5.
Fig. 14.6 Drops of water appear on outer
surface of the glass containing water with ice
The process of condensation plays an
important role in bringing water back
to the surface of earth. How does it
happen? As we go higher from the
surface of the earth, it gets cooler. When
the air moves up, it gets cooler and
cooler. At sufficient heights, the air
becomes so cool that the water vapour
present in it condenses to form tiny
drops of water called droplets. It is these
tiny droplets that remain floating in air
and appear to us as clouds (Fig. 14.7).
It so happens that many droplets of
water come together to form larger sized
Paheli has noticed dew on leaves of
grass on winter mornings. Did you
notice something similar on leaves
or metal surfaces like iron grills and
gates on a cold morning? Is this
also due to condensation? Do you
see this happening on hot
summer mornings?
Fig. 14.7 Clouds
Ice
Water
droplets
2022-23