You have to understand
that water comes in different forms, or states of matter.
There's liquid water, solid water (ice), and water as a
gas (water vapor).
Water is constantly being
recycled in the water cycle. Here's how it
Let's say you're painting
with watercolors. The paint is wet when you brush it onto
the paper, but later it dries. Why? The water molecules
in the paint escaped into the air. (They evaporated.)
These water molecules floating in the air are called
water vapor. You can't see them, but they are there. When
the water molecules in the paint escape into the air,
only the color remains on the paper.
What happens next? Well,
when warm air containing water vapor hits something cool,
the water molecules turn into a liquid. (They condense.)
That's why drops of water collect on the outside of a
cool glass. The cool air close to the glass causes water
molecules in the air to slow down and condense against
the side of the glass.
The back and forth
process of evaporation and condensation is called the
water cycle, and it is how the earth recycles water. When
the sun warms the earth, water evaporates into the air.
As the water vapor rises and meets cooler air, it
condenses back into water again, forming clouds and rain
which falls to the surface of the earth.