Water travels for long distances around the world. When the sun shines, the heat makes seawater evaporate. Seawater is salty, but the salt is too heavy to be carried upward by the water vapour. The fresh water begins its journey as a cloud, condenses to form rain or snow, and falls to earth again. Back on dry land, it flows all the way downhill and ends up in the salty sea again.
Ever since man first appeared on earth, we have been influencing nature. Our actions also affect the water cycle.
- We use water for ourselves and for industrial purposes. Then it’s not so clean any more.
- We also build canals and sewers to make rainwater drain away more quickly. This sometimes lowers the watertable.
- In places with hot climates, river water is stored in reservoirs and used for irrigation. Sometimes the river dries up completely as a result and never reaches the sea. Instead, the water evaporates from the land.