You already know that 72% of the planet's surface is covered with water. But there is still

water on the rest of the Earth, in streams, rivers, lakes and canals. Where does all this water come from?

Water always flows downhill, from a high place to a lower place. When a downpour hits a hill, the water falls on the soil, or trickles down the leaves of trees. Some of the water soaks into the earth and makes a water table. In building a deep cellar or an underground car park, the engineers can come across the water table.

The rest of the water runs over the soil and flows downhill. These rivulets meet others and, little by little, bigger streams are created.
When all these streams reach the valley, they unite and become a river. As valleys don't slope as much, the water moves more slowly. Whilst running down the mountain, the water carries stones, which eventually become sand and gravel at the bottom of the river, broken down by the action of the water. But first of all, these stones make barriers which force the river to wind...