Did you know that nearly three-quarters of the surface of the earth is covered with water? 
There are vast oceans like the Atlantic and the Pacific, and smaller seas like the South China Sea and the Red Sea.
There are lakes, rivers and streams.
Around the North and South poles, frozen water forms icecaps that last all the year round.
Below ground, there is even more water. 
This has soaked down through the soil to fill the spaces between the rocks with large stores of water.
There is even water in the air. 
Clouds are made up of millions of tiny droplets of water. Clear skies contain moisture which moves around in the air as an invisible gas.
Water is different from every other substance on earth because it can be found in its natural state in three different forms.

  • When we speak of water, we usually mean water as a liquid. 
  • When water is solid, we call it ice. 
  • When it is a gas, we call it water vapor.

Water can change very easily from one form to another.
Heat from the sun makes liquid water change to water vapor.
When the water vapor cools it forms rain, which falls to the earth.
If the rain becomes very cold it can change to snow or hail.
Every living thing on the earth depends on water.
Animals need water to drink.
They may eat other animals or plants, and these also need water to survive and grow.
Even plants and animals that live in desert regions, where rain rarely falls, need the tiny amounts of water vapor in the atmosphere to survive.