"Class 7 CBSE NCERT Science Ch -16 Water" Hope you will like it...

1. Science
WATER:A PRECIOUS RESOURCE

2. Introduction

3. Water is oneof themost common
and useful substances around us.
Water is essential for theexistence
of all forms of life
.After knowing
theimportanceof water
,
awareness is being created by
different organizations of the
world. 22nd March is celebrated
as World Water Day to attract the
attention of everybody towards the

4. importanceof conserving water.
Theyear 2003 was recognized as
the‘International year of
freshwater’.By doing such
activities,wespread themessageof
conservation of natural resources
of water and make people
understand that therewill beno
lifewithout water on theearth. We
also be
lievethat “if you havewater
,
you can think of thefuture”.
Beforewediscuss why water is
getting scarce,wemust know how
much water is availablefor use on
our planet.
WaterAvailablefor
Use

5. If wetake a pictureof earth
from outer space,it appears blue
because of thepresenceof water in
theform of thesea and ocean.
About 71% of thesurfaceof the
earth is covered with water
.Of the
total water present on earth,
97.fj% is in theseas and oceans
but it is not g t for human
consumption. Freshwater in a

6. usableform is present in just a
small fraction of all water present
on theearth. Most of us assume
that thereis plenty of water all
over theearth. But in fact this all
water is not suitablefor human
consumption, not even g t for
plants and other forms of life
.
Different Forms of
Water
Water exists in threeforms.These
threeforms of water areas
follows:
Snow or ice(solid)
Water (liquid)

7. Clouds (gas)
Snow or ice(solid)

8. Snow or ice(solid) exists on the
earth in theform of icecaps at
thepoles of theearth,glaciers,
and snow-covered mountains.
Thesearethemain sources of
water on earth.
Water(liquid)

9. Water (liquid) is present in
oceans, lakes, rivers,and even
underground water in theearth’s
upperlayers.
Clouds (gas)

10. Clouds (gas) arefound in the
form of water vapor present in the
atmosphere
.On condensation, it
turns into droplets and
precipitates on theearth’s surface
in theform of rain.
The continuous recycling of these
forms of water takes place and
theamount of water on theearth

11. is maintained constant. Most of
theurban areas havea syste
mof
water supply whereas
underdeve
loped/undeve
loped areas
depend on resourceslike rivers,
lakes, ponds,handpumps,etc.
Groundwateras an
Important Sourceof
Water
Thewells, tube-wells, and
handpumps arethemain sources
of water for many people
.The
water in thesesources is the
groundwater
.I t is theupperleve
l
of underground water that
occupiesall thespacesin thesoil
and rocks and form a water table
as shown in theg gurebe
low:

12. Theupperlimit of groundwater is
called water table
.I t represents
thedepth of a water-g lled area
at a given place.Thewater table
rises and falls depending upon
theamount of rainwater that
seeps into thegroundwater and
how much groundwater is drawn
out for irrigation and industry.
Theseeping down of rainwater
into thegroundwater is called
ing ltration. Thegroundwater thus
gets recharged by this process.At
someplaces,thegroundwater is

13. stored between layers of hard
rock be
low thewater table
.This is
an aquifer that contains the
groundwater usableby tubewells
and handpumps.Thesesources,
however
,havelimited sources of
water and may get exhausted if
used excessive
ly.
Depletion of Water
T
able

14. Water drawn from underground
water gets replenished by seepage
of rainwater
.Thewater tabledoes
not get affected as long as we
draw thesameamount of water as
is replenished by natural resources
like rain. However
,thereis a
number of factors which cause the
depletion of thewater tableat a
very fast ratewhich is really a

15. matter of concern for every oneof
us.An increase in population,
industrial and agricultural
activities are somecommon factors
affecting thewater table
.Scanty
rainfall, deforestation, and a
decrease in theeffectivearea for
seepageof water may also deplete
thewater table
.
Increasing Population
As our population increases,we
need morewater for drinking,
washing, cooking, and cleaning.
We also need morehouses,o ces,
shops, and roads.This means more
construction work and
construction itself uses lots of
water itself. Most of thetime
,it is
thegroundwater
.Besidesthis,there

16. is a less open area that can seep
therainwater into theground.
So,a rise in population also
increases theuse of water
.This
results in depletion of
groundwater leve
ls to alarmingly
low leve
ls (in many cities).
Increased
Industrialisation
Water is used by all industries.
Almost everything that weuse
needs water somewherein its
production process.Thenumber of
industries is increasing
continuously.Most of thewater
used in theindustries is drawn

17. fromgroundwater.This results in
depletion of water.
Agricultural Activities
Morefood is needed to meet the
requirement as there is an increase
in population. This puts more
pressureon agriculturepractices.
In our country
,farmers depend on
rain, canal water
,or groundwater
for irrigation. Canals arefound
only in a fewplaces.Sincerain is
often erratic,canals also suffer
frequently froma lack of water
.
Therefore
,farmers haveto use
groundwater for irrigation. This
results in depletion of
groundwater
.

18. Deforestation
Large-scaledeforestation has
occurred to accommodatethe
growing population to growfood
for the
m and to providespacefor
industries.Overgrazing by our
animals has also destroyed a
largeamount of vegetation. The
green coverageof vegetation slows
down the owof wateron land
and increases theabsorption of
water by thesoil. Cutting down of
trees and vegetation, therefore
interferes with thenatural
processes by which seepagetakes
placeand thegroundwater is
recharged and causes depletion of
water
.

19. Distribution of Water
Thedistribution of water over the
globeis quiteuneven dueto a
number of factors.Someplaces
havea good amount of rain. On
theotherhand, thesearedeserts
that havescanty rainfall. Some
regions haveexcessiverains which
cause oods whilesomeothers
havevery littlerainfall which
causes drought. India is a vast
country and therainfall is not
thesameeverywhere
.Therefore,
someregions in our country may
have oods whileothers may
sufferfromdroughts at thesame
time.

20. WaterResourcesin
India
India receives a lot of
precipitation (rain and snow) in
comparison to therest of the
world. Theaverageannual
precipitation in India is 1170
mm as compared to theworld’s
averageof 700 mm.Therain map
of India showing averagerainfall
in thedifferent parts of our
country
.

21. WaterManagement
I t is theactivity of planning,
deve
loping, distributing, and
managing theoptimum use of

22. water resources.I t is a sub-set of
water cyclemanagement. Water
supply pipes leaking and a lot of
water gushing out of thepipes is
thewastageof water
.I t is the
responsibility of thecivic
authorities to prevent such wastage
of precious water
.Mismanagement
or wastagemay also take placeat
the level of individuals. All of us
knowingly or unknowingly
wastewater
,weshould also take
careof it.Someof thesteps which
can betaken for theproper
management of water aregiven
below:
Rainwater Harvesting
Bawris
Drip Irrigation

23. RainwaterHarvesting
Most of therainwater just ows
away.This can beskillfully used
to recharge thegroundwater
.The
modern buildings of schools,
o ces,homes can install a
rainwater harvesting syste
m,so as
to storerainwater in their own
pre
mises for futureuse.
A Case Study

24. Bhujpur in theKutch area of
Gujarat has a very erratic
rainfall. Theonly sourceof
freshwater lies underground
because rivers in this area do not
havewater throughout theyear
.
Over theyears,de
mand for water
has grown.As a result, thewater
tablehas gonedown alarmingly.
In 1989,thevillagers along with a
non-governmental organisation,
decided to harvest rainwater
.
Eighteen check-dams werebuilt
on theRuhmavati river and its
tributaries wherewater percolates
through thesoil and recharges the
aquifers.According to farmers,
thewells havewater now and the

25. water that owed into thesea
and was wasted has becom
e
availablefor irrigation.
Bawris
Thebawris is an age-old method
of collecting water
.Thesestructures
arestill found in old buildings,
palaces and forts.With time
,the
bawris fe
ll into disuse and
garbagestarted piling in these
reservoirs.However
,because of the
acuteshortageof water
,thebawris
arebeing revived. T
oday the
situation is that inspiteof scanty
rains those places aremanaging
their water needs well.

26. Drip Irrigation
I t is a method of watering plants
by use of narrowtubings which
de
liver water directly to thebase
of a plant.This minimizes the
wastageof water
.Themechanism
of drip irrigation is shown in the
g guregiven be
low:

27. Rolefor Saving Water
You can bea leader to show people
water management skills. If any
pipe
lineand tap water are
leaking there
,immediate
ly report
to authorities like ‘JALBOARD’(in
Delhi) to prevent water loss.
Educatepeopleabout water-wise
habits which can bedeve
loped
gradually and will last lifelong
oncedeve
loped.

28. Water-wiseHabits
T
urn off thetap whilebrushing,
shaving,and washing your hand.
Open when need. This will check
theexcess owof water into
drains. Use mug and water in the
bucket for bathing instead of
using showers.Mop the oor
instead of washing.Irrigate
potted plants with used water for
washing riceand dal in the
kitchen whilecooking.Check no
tap or pipeis leaking.
Effectof Water
Scarcity on Plants

29. We growmany plants in pots in
our homes.Thesearecalled potted
plants.Thepotted plants are
watered regularly.If thepotted
plants arenot watered even for a
fewdays,theplants will ‘w
ilt’
(becom
elimp) and ultimate
ly ‘
dry
up’. If potted plants arenot given
water for a considerabletime
,they
will die
.Thus,su cient water is
essential for maintaining thelife
of plants.Plants need water to
obtain nutrients fromthesoil and
to make food by theprocess of
photosynthesis.Thevarious effects
of water scarcity on plants are
Water scarcity will affectnutrient
uptake fromsoil by theplants.
Therateof photosynthesis will
decline
,so oxygen evolved will be
less.Therateof transpiration will
also decline
,so watervapors

30. re
leased in theatmosphereby
transpiration will beless,it will
disturb thewatercycle
.So,in brief,
wecan say theshortageof water
will lead to a shortageof food,
shortageof oxygen,and shortage
of rain also.

31. Thank You!!

32. CREATED BY
Ananya

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