Water cycle, illustration. The Earth's total water supply is estimated to be over 1.3 billion cubic kilometres. The arrows (blue) show some of the ways by which this water is redistributed. This includes evaporation from oceans and land to form clouds (across top) from which rain and other forms of precipitation fall, often over mountains (upper left). The water then forms rivers and streams over land, as well as snow, ice and glaciers in the mountains. Water also flows underground into water tables or to the sea. Plants take up water from the soil and release it into the air by transpiration.