Water or H2O has some very interesting properties. It is one of the few chemical substances that can be found it all three states – solid, liquid, and gas – at the same temperature and pressure. Transparent, tasteless, odorless and nearly colorless, is a necessary element in all know life forms. Water vapor makes from 0 to 4 percent of the atmosphere, depending on location, season, and time of day. For example, in the cold, dry Arctic regions, it is generally less than 1 percent. In humid, tropical regions, water vapor may comprise as much as 4 percent of the atmosphere.
Mary Knapp, Weather Data Library