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| Water |
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| About 70-73% of earth is covered by water. Water is available in the form of oceans, seas, rivers, lakes, ponds, pools, polar ice caps and water vapour. The main component of hydrosphere is water. Water exists in all the three forms i.e., solid (snow), liquid (water) and gas (water vapour). |
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| Water is absolutely essential for the maintenance of life. The most important character of water is that its density is similar to that of protoplasm. Water consists of two atoms of hydrogen and one atom of oxygen. It is a universal solvent since it dissolves most of the compounds. |
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| Water is the fundamental natural resource. Human beings depend on water for drinking, cooking, agriculture, transportation, hydropower etc. |
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| Water available in nature is of two types. |
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| Salt Water: It constitutes the oceans and the seas. Nature has comparatively more salt water than fresh water |
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| Fresh Water: Fresh water is an unlimited natural resource. Its quality is often degraded but there is no reduction in quantity. |
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| There are three main sources of fresh water. |
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 Rainwater |
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 Surface water (surface flow) |
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 Ground water |
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| Rainwater |
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| India receives about 3 million m3 of water from rainfall (or precipitation), which amounts to 105-117 cm annually. This is a huge quantity and the largest in the world. |
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| Intensity of rainfall in India varies from region to region forming four zones. They are: |
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| Wet Zone: Here annual rainfall is very high (i.e. over 200 cm). West coast of India and northeastern parts of India come under this category. |
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| Intermediate Zone: Rainfall is quite heavy (i.e. 100 to 200 cm). Parts of UP, Karnataka, Maharastra, Bengal, Orissa, Punjab, Himachal Pradesh and Kerala fall in this zone. |
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| Semi Arid Zone: Annual rainfall is moderate (i.e. between 50-100 cm). Most parts of central India, Southern peninsula and parts of Rajasthan and Gujarat comes under this region. |
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| Arid Zone: In this zone the annual rainfall is very low (i.e., it ranges from 20 to 50 cm). Rajastan and parts of Gujarat fall under this region. |
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| Surface Water |
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| In India, there are 14 major river systems such as Ganga, Brahmaputra, Godaveri, Krishna and Cauvery. The other sources are ponds, lakes and streams. |
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| Ground Water |
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| Underground reservoirs of fresh water are called aquifers. They are continuously recharged through infiltration, sewage and evapo transpiration. The total volume of ground water found in the aquifer is estimated to be 42.3 x 1010m3. |
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 The space between soil particles on the surface of earth is called pore space. This is of two types, micro pores and macro pores. Most of the water is held in the micro pores. These pores are available for plant roots |
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| Surface soil pore spaces are generally filled with air and water. Water that percolates down through pore spaces of rocks is available as ground water. This ground water provides soil moisture for plants and supplements streams and lakes. |
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| The porous rocks are saturated with water at a certain level below the surface that is called zone of saturation. The upper level of zone of saturation is called the water-table. The depth in the soil where all the pore spaces of soil particles are saturated with water is called water table. The water table reaches the surface of earth in rainy seasons, near rivers, lakes and swamps. It is deeper on hilltops, in dry areas and in areas of low rainfall. |
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| The following factors tend to lower the water at any given place |
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 Scanty rainfall |
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 Excessive use of ground water |
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 Cultivating of trees |
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 Hygroscopic and Capillary water: Water, which is retained around the soil particles |
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 Gravitational water: Water, which is free to drain downwards through the soil |
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