General Astronomy/The Water Cycle
All of the water in the world keeps getting reused and reused. Why? Water molecules can be made into three forms: gas (steam), liquid, and solid (ice). The water cycle turns water into all three of these forms.
the Cycle 
Part 1: Up 
Water starts in the oceans. The oceans contain tons of water, and there is more water than land on the Earth's surface. With all this water in the same place, the water turns to steam, or evaporates. And since steam is lighter then liquid, it goes up.
Part 2: Together Again 
Now in the sky, the water condenses.