The total quantity of water in the world is 1357.5 M cukm.
97% of total water in the world is contained in oceans as saline water.
The total amount of rain and snow falling on the earth each year about 0.42 M Cukm.
Each year the rivers of world discharge about 38,000 cukm of water into the sea.
The worlds largest river the Amazon, has an average discharge of 2000,000 Cum/s.
Over the oceans 9% more water evaporates  than falls back as rain, to be balanced by the excess ppt. over the land masses.
It is interesting to know that less than 4% of the total river flow is used  for irrigation while rest flows to sea.
The volume of water carried by rivers and springs to the sea each year is about 0.038 Mcukm.
The amount of water vapour present in the atmosphere is about  0.013 MCukm.
The amount of ground water present below depths of 800m is about 4.150 MCukm.
India's largest river,the Brahmputra, and the second largest Ganga flow into bay of Bengal with mean annual discharges of  16200 cum/s and 15600 cum/s resp.
Most of the present day Hydrology has been developed since 1930, giving it the status of young science.
History has instances of civilization that flourished with the availability of dependable water and then collapsed  when the water supply failed.
