A drainage basin is the area of land that it drained by a river and its tributaries. When a droplet of water falls onto the land (as precipitation), gravity will make sure that the water is ‘pulled’ downhill to return to the sea.
The water cycleis also known as the hydrological cycle.
Seas and oceans contain 97% of the world's water, and ice holds 2%.
That leaves just 1% of the world's water as fresh water on land or in the air.
This water is recycled again and again through the process of evaporation, condensation and water transfers such as surface runoff.