The protagonist of this episode is water: through a story that will take us from the origins of life on Earth to biology, from engineering to molecules and art. With the help of graphics we will be able to simulate a journey inside a drop of water to discover its composition and microorganisms. We will then follow the long paths taken by water, through extraordinary images of glaciers, caves, oceans, atolls, icebergs, discovering how rivers are born, how raindrops are formed. We will also discover the effects that water produces in our body and how much we need for our survival. Alberto Angela will go to Villa d'Este in Tivoli to show us the works of artists and architects who over the past centuries have created an immense complex of water features and fountains on an entire hill; and again at Niagara Falls, where we will be able to admire one of the most magnificent spectacles that exist in nature.