### Theory:

In the previous grades, we studied that oceans are massive bodies of water. Have you ever wondered how much water does the oceans together have? Could you imagine such a massive amount of water? In this unit, let's discuss the amount of water in various forms, sources of water and amount of water each source has.

Earth is rightly termed as a watery planet because about$$71$$% of the Earth's surface is covered by water. The total quantity of water present on the Earth is about $$326$$million cubic miles. It is hard to imagine such a massive quantity of water. But, all of them are not available for us to drink or use for domestic purpose.

Most of the water on the Earth is saline and is found in seas and oceans. Out of the total water content, saltwater constitutes about $$97.2$$%, and freshwater is only about $$2.8$$%. Even out of this $$2.8$$%, about $$2.2$$% is available as surface water and the remaining $$0.6$$% as groundwater. From this $$2.2$$% of surface water, $$2.15$$% is available in the form of glaciers and icecaps, $$0.01$$% in lakes and streams, and the remaining $$0.04$$% is in other forms. Only about $$0.25$$% of the total groundwater of$$0.6$$% can be economically extracted with the present drilling technology. Water resources are useful or potentially useful to humans. Three different sources of water available in India are precipitation, surface water and groundwater.

Estimated Volume of Water on the Earth’s Surface
 Water Source Volume of water (Cubic miles) Percentage of Total Water Oceans, Seas & Bays $$321,000,000$$ $$96.54$$ Ice caps, Glaciers & Permanent Snow $$5,773,000$$ $$1.74$$ Groundwater $$5,614,000$$ $$1.69$$ Soil Moisture $$3,959$$ $$0.001$$ Ground Ice & Permafrost $$71,970$$ $$0.022$$ Lakes $$42,320$$ $$0.013$$ Atmosphere $$3,095$$ $$0.001$$ Swamp Water $$2,752$$ $$0.0008$$ Rivers $$509$$ $$0.0002$$ Biological water $$269$$ $$0.0001$$