Have you ever heard someone refer to water as H2O? Why do you suppose someone might call water by this name? What is water? Water is a basic molecule made up of two hydrogen atoms and one oxygen atom. When these three atoms come together, they form a strong bond that is difficult to break. The strength of this bond keeps a water molecule together for millions and even billons of years.

Water is one of the most common substances on the Earth. Covering over 70% of the surface of the Earth, it is easy to find. Even in a desert it is not hard to find water, if you know where to look.

Scientists believe that the amount of water on Earth does not change appreciatively over time. In other words, the amount of water that is on the Earth today is the same amount that was on the Earth during the reign of the dinosaurs.