Water is a vital natural resource which forms the basis of all life. Water is a key resource in all economic activities ranging from agriculture to industry. Places where lack of food threatens human survival, it is the lack of water that limits food production. Water also plays an important role in the development of earth’s surface, moderating climate and diluting pollutants. Without water, life as we see cannot exist. It is an essential ingredient in the photosynthesis of plants which becomes food for various living systems. Atmospheric humidity which constitutes water is highly essential for all terrestrial life to protect from dehydration.
Only a small fraction of the abundant water is available as fresh water because 97% is present in oceans as saline water and out of the remaining 3% about 2.997 % is locked up in ice-caps or glaciers or buried so deep making it too difficult to extract. Thus only 0.0035 of Earth’s total volume of water is available to us as soil moisture, exploitable ground water, water vapour, and lakes and streams.
In India, out of the total rainfall in an area of 3290 lakh hectares, a rainfall of 4000 billion cubic meters annually occurs. Out of these 41% is lost by evaporation, 40% is lost as run off, 10% gets retained as soil moisture and 9% seeps in for recharging ground water. Out of the 40% stream flow water, 8% is used for irrigation, 2% for domestic use, 4% for industry and 12% for electricity generation. Thus out of the total available water resource of 1869bcm, the usable water resources are only 1122 bcm, which consists of surface water 690 bcm and ground water 432 bcm. The present per capita available water resources is 1122 cm and by 2050 it is likely to reduce to 748cm. Countries whose per capita water availability is less than 1700 cm is considered as water stress country.
Major rivers in India can be classified as (i) Himalayan water system (Indus, Ganga, Brahmaputra, Chinab, Jhelum, Ravi and Beas) (ii) Deccan Plateau water system (Narmada, Tapti, Mahanadi, Godavari, Krishna, Periyar) (iii) Coastal water system and (d) others including inland water systems.
Source: Introduction to Environmental Science, Y. Anjaneyuly, BS Publications.