Water is absolutely essential for all forms of life. We experience this every day when we become thirsty. Why do we need so much water? Simply because our bodies consist of approximately 75% water. If we do not drink enough water we may dehydrate.
The same water that is used presently was used by the dinosaurs millions of years ago. This is because the Earth recycles its water, i.e. it re-uses the water. This recycling of water is called the water cycle.
Water exists on Earth as water droplets and is found in oceans, rivers, lakes, dams, the soil, and other places. Heat from the sun causes some of these water droplets to change from a liquid to a gas, called water vapour. This process is called evaporation.
The water molecule is one of the most versatile structures known. Comprising two atoms of hydrogen and one of oxygen (H2O), water has remarkable dissolving powers and is therefore a supreme solvent. Changing from solid to liquid to gas, water absorbs large amounts of energy in the form of heat, and releases equivalent amounts when going from gas to liquid to solid.