ü  The water is very important for all forms of life.

ü  The chemical symbol of water is H2O.

ü  Water is a chemical substance.

ü  H2O contains two Hydrogen and one oxygen atoms.

ü  Water is liquid.

ü  The solid state of water is Ice.

ü  The gaseous state of water is stream.

ü  The water is mainly available in 3 forms.

v  Ground water

v  Surface water

v  Ice cap and Vapor.

ü  The water moves from one pool to the other and is called Hydrological cycle or water cycle.

ü  (Note: We all know that through rain we get water on to the earth, oceans etc. The same water evaporates and reaches the atmosphere again precipitates and rains on the earth. This is Hydrological cycle).

ü  Evaporation: This is the transition of water from liquid state to gaseous state.

ü  Transpiration: This is the diffusion of water into the atmosphere.

ü  Through evaporation and transpiration water is added to the atmosphere.

ü  The amount of water that is added to the atmosphere through evaporation and transpiration and the amount of water that is returned to the earth in the form of precipitation (rain) is equal. This is how the global water balance is maintained.

ü  (Note: the important forms of precipitation are rain, snow, hail, sleet etc).

ü  Oceans are the largest reservoirs of the water.


ü  Out of the total water that is available on the earth more than 97 percent is present in the oceans.

ü  Ice caps and glaciers account for 2.15 percent of water.

ü  The ice caps are the largest reservoirs of fresh water.


ü  The atmosphere contains only 0.001 percent of water.

ü  The amount of the ground water is only 0.635 percent.

ü  The total mass of water put together is called Hydrosphere. (Water covers 71 percent of the earth surface. Out of this the oceans constitute the majority of the water, Regarding Oceans we discuss later).



Does all the water precipitating from the atmosphere reach the earth?

v  The answer is “No”.

v  Some amount is evaporated in the atmosphere.

v  Some part will be in the form of snowfall.

v  A part is absorbed by the soil in the form of soil water.

v  The remaining water flows over the surface and reaches the sea or ocean and is called runoff water.

v  Did you hear Water harvesting? Why is it done?

v  Did you hear some places become dry and the people suffer with lack of drinking water? Do you know why?

v  In some area there is no harvesting of crops because of lack of water. Where is the water?
v  Please think about this, we answer at a later stage.

Now let us try to know some important terms.

v  Percolation: This is a process of water entering the rocks. This happens after the soil is saturated. Percolation depends on porosity and permeability.

v  Porosity: This is the presence of pores in the rocks.


v  Permeability: The capacity of the rock to allow water to move from upper parts to the lower parts.

v  Ground water: The water that is percolated and available in the rocks is called the ground water.

v  Connate water: This is the water that is present in the rocks since its formation.

v  Zone of saturation: The area of the rocks where the pore spaces are completely filled by water.

v  Water Table: It is the uppermost surface of the Zone of saturation.


v  Aquifers: The rocks of the earth that contain water. (These rocks are porous).

v  Aquicludes: The rocks that do not contain any water. (These rocks are non porous).

v  Seepage: This is a limited flow of water on to the ground from a spring.

v  Geyser: This is a periodic jet of hot water and steam. (Old Faithful is a geyser. This is present in Yellowstone National park in USA. This ejects every 65 minutes).


v  Artesian well: The water comes to the surface on its own without any pressure.

*      Are the porosity and the permeability permanent? No, over a period of this is decreased?

·         As more water percolates the pore spaces will be clogged.

·         The mineral particles will expand because of the absorption of the water and the porosity is reduced.

ü  The water that is present in the ground is not perfectly horizontal.

ü  There are slopes.

ü  When a water table intersects the ground a spring is formed.

ü  If the hot water emerges out of a spring then it is called hot spring.

ü  If the spring contains minerals then it is called mineral spring.