A water molecule is called "H2O"

It's made of 2 hydrogen atoms (H + H) and one oxygen atom (O). H2O can be a VAPOR (a gas in the air), a LIQUID (what we usually think of as water or a SOLID (ice).

The sun is the "pump" that keeps water going around and around. To learn more, find H2O's path through the water cycle, starting in the center at number 1. When you get to each stage in the cycle, read its numbered explanation at the bottom of the page.

1. Water vapor gathers in clouds. Wind cools the vapor, turning it into a liquid (rain) or solid (snow, hail or sleet).
2. Gravity makes the water fall to earth.
3. Some water runs across the land into bodies of surface water -- lakes, streams, oceans, etc.
4. Other water soaks ("percolates") into the ground.
5. Percolated water is stored in the ground in "aquifers" (layers of rock, gravel and sand). This ground water slowly moves through the aquifer toward the sea.
6. Eventually, ground water becomes surface water, too. For example, it may bubble up through the ocean floor, or appear on the land as a spring.
7. The sun heats surface water, turning it into vapor that rises into the sky. And the cycle begins again!