Our Earth
is covered by two-thirds of water, but most of the water is not potable and
contains salt.
Sources of Water
Ponds,
wells, streams, lakes and rivers are the different sources of drinking water.
They are supplied water by the oceans and seas. Oceans and seas supply water to
other water bodies through the water cycle.
Water Cycle
The
circulation of water from the oceans and the surface of the earth, to the air
as water vapour and its return to the ocean as rain, hail or snow, is called
the water cycle.
The
evaporation of water takes place in the water cycle, leaving the salts behind
in the ocean. The water present on the surface or the ocean evaporates by the
sun’s heat. This process of conversion of water from liquid state to vapour
state is called evaporation. Evaporation takes place faster in direct sunlight,
than in a shady area.
Plants take
in water to grow as well as to prepare their food. They retain the water they need and release
the excess water into the air as water vapour through the stomata of the leaves
and the stem. This process is called transpiration. Thus, water is mainly
evapo-transpirated to the air from land, water bodies and plants.
The
evaporated water is carried away by warm air. As the warm air moves higher from
the surface of the Earth, it starts to cool down. It is because the water
vapour present starts to condense to form tiny water droplets. These droplets
float in the air and form cloud and fog. All these droplets collect to form
bigger drops of water. Some of them may become too heavy to remain in the sky
and fall down as rain. This process is known as precipitation.
If the air
is too cold, the water drops can become snow or hail and may settle on the top
of a mountain. When these snow or hail melts, they can become part of a river
or a stream. Thus, the water that is evaporated from the oceans or seas is
again condensed to form water and fills up the rivers and seas. Rain water also
seeps into the ground to form ground water.
This
circulation of water is called the water cycle.
Uses of Water
Water is
used in our day to day life.
• Water is used for everyday needs such
as brushing, bathing, washing, cleaning etc.
• Farmers use ground water to water
their fields.
• Many industries use ground water to
produce everything from paints and fabric to leather and chemicals. So ground
water is used for many purposes.
Moreover
the decline in the number of trees, excess usage of water and the presence of
concrete in the areas does not allow the rain water to seep into the ground
which is the reason for the shortage of water.
Droughts
Due to lack
of rains the wells, lakes, ponds get dried up and thereby creating water
scarcity and as result droughts are possible. If there are no rains, then the
soil becomes more dry and patchy.
Droughts
occur when there are no rains for a longer period of time. Droughts results in
drying up of the crops and vegetation and this effects the availability of food
and fodder.
Floods
Due to heavy rainfall the water levels in
ponds, lakes rises to a greater extend and the rise in the water level of these
water bodies causes the excess water to spread across causing floods.
Floods wash
out the living beings such as fish and other animals etc. and they create great
havoc to the mankind. Floods cause extensive damage to crops, domestic animals,
property and human life.
Rain Harvesting
Harvesting
is a method to collect rain water and store the rain water. The purpose of
harvesting rain water is that two-thirds of the earth is covered with water.
Ocean and sea water contains many dissolved salts and cannot be used for
drinking, agriculture and domestic purposes. So, constant use of groundwater
results in scarcity of groundwater. Rain harvesting clears the problem of
depleting the ground water.
Technique involved in rain harvesting
First
collect the rain water at the rooftop and then allow the rain water to travels
through the pipes or drains and then attach a wire mesh to the mouth pipe which
filters large fragments such as leaves etc.
This water
is transported to the water tanks. These tanks contain layers of sand, gravel,
charcoal that will filter the dirt and other impurities from rain water. The
water stored in the tank will then be transported to an underground pit which
will help water to seep back into the ground.
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