Rain and snow are the main sources of fresh water for people living on earth. Both rain and snow come from the clouds; but, where do the clouds come from? It often seems that clouds appear from nowhere. One minute the sky is clear and then a few minutes later clouds form. Sometimes clouds come from far places. Wind moves the clouds from one area to another.

If you live near a lake, ocean or forest, you may have seen water vapors rising from wet surfaces and disappearing in the air. Is it possible that the same vapors become visible again when they get to higher elevations? If the clouds come from oceans, forests and other surface waters, then why doesn't the rain water contain salt and other pollutants that exist in rivers and surface waters?