Some water molecules are moving faster than others. Sometimes the fast ones can break free and escape into the air as water vapor. That’s what we call evaporation. It happens faster with higher temperature, but it can happen any time you have liquid water with not too humid air.
Water vapor molecules in the air also move around, and if they hit the surface of liquid water, or other surfaces, especially cool surfaces, they can get stuck. This is why your bathroom mirror gets foggy after a hot shower.
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