Water is our precious resource. Although the planet has more water covering it than land, only a very tiny fraction is usable for things like drinking. On top of this, the fresh, usable water is not distributed equally over the planet. People have a big impact on this freshwater. Oil, sewage and pesticides are making much of this usable water unusable.
The hydrological cycle describes the three states of water on Earth and describes how water moves over the planet. People impact this cycle in many ways, causing changes to how water moves on our planet.