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

        found in polar regions or higher altitudes. It remains

        frozen for a long period of time. The oldest

        permafrost that remains frozen for 700,000 years

        is located in Siberia.