Introduction back to top Water is the most important substance on Earth. Without it, there would be no plants, no animals, no life. As we are constantly losing water we need to take in more to replace it. Of the fresh water, most is frozen in the polar ice caps. As we use this water, it is replaced by natural processes - part of the water cycle .
Water has many unusual properties, and is a special compound because many substances dissolve in it.
This means all the special molecules that make up you and me and all other life can meet together in solution and react. Most of the water in water cycle is in the oceans and seas of the world. This also happens to water on land, in rivers and lakes, and from the leaves of plants, when it is called transpiration . This causes the air to rise, taking the evaporated water with it. As the air rises, it cools, and can no longer hold as much water.