Moisture
When it rains we are made aware of just how much water the air contains. Much of the time, this water remains hidden as water vapour or moisture. It becomes visible for the first time when clouds form.
Clouds are made up of very small water droplets which are suspended in the air. Under the right weather conditions small cloud droplets will join together to form larger droplets. Eventually the weight of the water drops may be heavy enough to make them fall as rain.
The air loses a lot of water through rainfall, but the atmosphere does not dry up. Moisture is returned to air by a process called evaporation. Water evaporates from oceans, lakes, rivers and ponds on the Earth's surface, and in fact any body of water that may be present after the latest rainfall. This cycle of evaporation, cloud formation and rainfall is called the water cycle, and is essential for life.
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