There is always water vapor in the air, but the individual water molecules are so tiny that you can't see them. Water in the air is invisible unless it forms tiny water droplets (fog) or bigger ones (rain) or freezes (snow crystals). Here's one way to picture it.

Look at the three boxes below. What do you see in each box?
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L5: Write your response in the box below. L4: What do you see in Box A? What do you see in Box B? What do you see in Box C? L3: Box A looks like... Box B looks like... Box C looks like... L2: Which box looks the most "clumped?" L1: Box A looks like one big clump, Box B looks like five medium clumps, and box C looks spread out.

Now look at the three boxes up close. What do you see in each box?

Each box has 20 dots in it. When they are in large groups (Box A) it is like rain droplets, and you can see them. When they are in small groups (Box B) it is like clouds or fog. When they are spread out (Box C), it is like water vapor. The individual molecules are invisible to our eyes because they are so small.

• Water vapor, the form of water that is a gas, is released by plants (transpiration) and evaporates from lakes, the ocean and the surface of the Earth.
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• When conditions are right, water turns back into a liquid in the form of tiny droplets.
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• As the tiny droplets form, they start to clump together and increase in size. When the droplets are big enough, they fall to the ground as precipitation.
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