Water-A Wonder Liquid

• Earth is the only planet where water is found in liquid form too and thus it supports the survival of living organisms.
• It is essentially required for the survival of living organisms including all plants, animals and micro organisms.
• Major portion of a living cell/ system is comprised of water and all cellular processes occur in water (aqueous) medium.
• It helps in transportation of various materials in a living system.

Occurrence of Water Resources:

• Water covers 75% of the earth’s surface in different forms. It exist on earth in 3 different forms:
• Solid state- ice/ snow frozen in polar ice caps and the glaciers, like those in the Himalayas.
• Gaseous state- water vapors in atmosphere.
• Liquid- water in oceans, sea, rivers etc.
• Most of the water found on earth is saline while some is fresh water which is found in different sources.

Distribution of Water Resources:

• Although the water is present abundantly on earth but only limited amount is available for consumption by living organisms (especially human beings) for different activities.

• 97% of total global water is saline and thus not available for human consumption due to high salt content. It is found in Oceans, seas and other saline inland water bodies.
• Fresh water accounts for only 3% of the total estimated global water supply. Of this percentage, 70% of the fresh water is frozen in polar ice caps and the glaciers, like those in the Himalayas.
• 29% fresh water is blocked in inaccessible areas under the ground thus not directly used by human beings.
• The fraction of fresh water available for humans is estimated at less than 0.003% of the total global water availability.
• Thus conservation of water is required to maintain the level and availability to human beings.

Sources of Fresh Water:

Rainfall:

• The first one is rainwater (or precipitation) is one of the sources of fresh water.
• India receives an overall rainfall of about 105 to 117 cm annually is collected on earth in the few months during monsoon season.
• This is a huge quantity and is the largest in the world.

Surface water:

• The second source is surface water; there are 14 major river systems such as Ganga, Brahmaputra, Godavari, Krishna and Cauvery.
• Nearly all major Indian rivers have dams on them for redirecting water for irrigation and for hydroelectric power generation.
• Other surface water sources include ponds, lakes and streams.

Underground water:

• Underground water is the water that percolates down the surface soil into spaces between the rocks.
• Ground water provides soil moisture for plants and supplements for streams and lakes.
• It is a reserve supply of water that the agricultural sector and urban water supply sectors are tapping increasingly.
• The water table indicates the level at which ground water is found and rises and falls according to the level water that percolates down to this level during the rains and the amount that is pulled out from it.
• In spite of vast irrigation networks and dams, groundwater is being over-exploited; most of the increase in irrigation capacity in India, in the last two decades has come from groundwater (84%). Regeneration is far slower than today's consumption trends and the water table of most Indian cities and many agricultural areas is on the decline.