Explain the availability and existence of water?

Water occupies a very large area of the Earth's surface and is also found underground. (i) Some amount of water exists in the form of water vapour in the atmosphere.
(ii) Most of the water on Earth's surface is found in seas and oceans and is saline.
(iii) Fresh water is found frozen in the ice caps at the two poles and on snow-covered mountains.
(iv) The underground water and the water in rivers, lakes and ponds are also fresh.