Water is a key compound for life on Earth. All living organisms need water. Some can survive in a dormant state without it for long periods of time, but all organisms will eventually die without it.
Water is constantly recycled. Energy from the Sun evaporates water from the land and sea forming water vapour. This rises up into clouds and then cools, condenses and falls as rain onto the ground. The water then drains into the sea and the water cycle starts again.
These are the key processes in the water cycle.
|Process||What happens to water|
|Evaporation||Water turns from a liquid to a gas when it evaporates. Energy from the Sun can evaporate water from all places on the Earth's surface such as puddles, ponds, lakes and oceans.|
|Condensation||After evaporation water can cool and convert from gas to liquid, often forming clouds.|
|Transport||Water within clouds can be blown many miles by strong winds and so transported to other areas.|
|Precipitation||Precipitation occurs when rain, snow, hail and sleet fall from the sky.|
|Surface runoff||Much water will be absorbed into the ground after precipitation but if a large volume falls or the ground is already wet some water can run along the surface of the ground.|
|Infiltration||This occurs when water that has fallen as precipitation is absorbed into the ground. This can then be stored within underground rocks called aquifers.|
|Transpiration||Plants need to maintain a constant stream of water to their leaves for transport and support. They allow some water to evaporate as water vapour from their leaves so it is continually 'pulled' to their leaves from the soil.|