Wikijunior:Big Book of Fun Science Experiments/Why does it rain?

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The surface of the Earth is about three parts water and one part land. Seas, oceans, lakes, etc., are some of the water sources. In the summer season the water in these water sources gets heated up which turns some of it into water vapor (gas). When the air is full of water vapour, clouds form. When the air cools down, it can't hold as much water, so the vapor turns back into liquid water - and it rains.