The Watercycle

Water has three states - ice, liquid and vapour. The proportions of the water on our world that is tied up in each state helps determine our sea levels. Under what we think of as normal conditions about 2/3 of the Earths surface is covered in water. 97 % of the this water is tied up in the salty oceans, the other 3 % is in freshwater rivers and lakes. Glaciers and Ice caps also hold a lot of water but a lot of this is tied up as it remains frozen for a long time. The atmosphere also contains water in the form of vapour and droplets.

The water cycle is the term we use to describe the movement of water between the Earth's oceans, the atmosphere and the land.This is a complex process so we use a fairly simple model to define the basic features of the cycle.

Some water may charge round the cycle, especially in temperate or tropical areas, but some may remain trapped in parts of it for a long time - thousands or even millions of years. This can be in ice sheets or glaciers, as ground water ( held within tiny spaces in soil and rock) or within the seas as only a tiny proportion of sea water is evaporated.