Around 70 per cent of the Earth's surface is covered by water, in oceans, seas, lakes, rivers and swamps. An interesting property of ice is that it freezes from the top down. Have you or someone in your family ever left a bottle in the freezer. Unfortunately for us, most of the water on Earth is salty or frozen. Only a very small amount is suitable for us to use in our day to day lives.
Water is the most important and probably the most widely known substance on Earth.