The water

is a substance the molecule consists of two hydrogen atoms and one oxygen, is essential for the survival of all known forms of life. From the physical standpoint, the water flows constantly in a cycle of evaporation or transpiration (evapotranspiration), precipitation, and moving towards the sea. The winds carry as much water vapor as it is poured into the seas through its course on earth, in an amount of about 45,000 km ³ per year. On land, evaporation and transpiration contribute 74,000 km ³ per year to cause precipitation of 119,000 km ³ each year