How does the water cycle work?

Heat from the sun causes water to become a gas, or vapour. This is called evaporation. As the earth's surface warms, rising currents of air carry the water vapour upwards. The water vapour becomes cooler as it rises, and condenses into tiny drops, forming clouds. These drops join together and fall back to the earth as rain, hail or snow. Rainfall may:

• evaporate directly from water, land or vegetation
  
• run off the land into streams and wetlands
  
• soak a little way into the ground, be absorbed by plant roots and then return to the water vapour in the air by evapotranspiration from the leaves of plants.
  
• soak deeper into the ground and add to the groundwater supply, moving slowly along the direction of groundwater flow towards rivers, wetlands or the sea.
  

This cycle has existed since water was formed on earth, but human activities change the way water moves through the landscape.