Water on Earth
71% of the earth is covered by water. 97.5% of the
total water is contained in the oceans. The rest
(2.5%) of the water is found in air as water vapour,
rivers and lakes, ground as soil moisture and in
aquifers. The total amount of water contained in
earth is conserved that means a very little amount
of water ever enters or exits the earth's atmosphere.
We get the fresh water from ice caps, glaciers,
ground water, surface water (e.g. lake, river,
wetlands), permafrost etc.
Ground Water
The groundwater is stored under the surface of earth
in aquifers. The water moves easily in an aquifer.
The aquifers are surrounded by the layers of porous
rock and soil. There are two types of aquifers:
confined and unconfined aquifers. The unconfined
aquifers are exposed to the surface of the earth.
As a result this type of aquifer comes in contact with
the atmosphere, meteoric water and other surface
contaminants. The upper part of this aquifer is called
the water table. On the other hand the aquifers
trapped between permeable and impermeable layers
are called confined aquifers. Water in this aquifer is
less affected by the surface conditions. If a confined
aquifer is surrounded by impermeable rocks or clay,
then the water pressure inside the aquifer becomes so
high that the water comes out to the ground naturally.
It is called artesian well.
Refill and discharge of the groundwater
The rain water or melting snow seeps down through
the cracks and the crevices of the surface of the earth.
Then it is stored underground in the aquifers. This
water flows out to the surface through springs, lakes.
This groundwater also discharges through the man
made pumps, wells etc.
Other sources of water
Glaciers and Ice caps:
Almost 10% of the world's landmass is covered
with glaciers and ice caps.
In a Glacier, the snow accumulates over a long
period of time and changes into ice. Snow
accumulates each year and therefore the glacier
becomes heavy and moves downward. It is a
river of ice. Ice caps are also glaciers and spread
out in dome like shape to resist downward fall.
Glaciers and ice caps provide fresh water.
Permafrost is a frozen (below 0 degree) ground
