|MadSci Network: Chemistry|
Water boils at 100 C at sea-leavel. This means that water vapour can exist at and above 100 C. If you bring the water to a higher altitude, say Denver, water will boil at a slightly lower temperature, so you would have water vapour below 100 C. If you heat the water vapour above 100 C it will still be vapour, but at a higher temperature. So water vapour can exist at any temperature above the boiling point of water. The boiling point depends on the pressure, which in turns depends on the altitude.
Also note that you can have water vapour at lower than 100 C temeperatures, even at sea level. Every liquid has a "partial pressure" which describes an equilibrium between the liquid and the vapor phase.
Thus, even at room temperature, you can still have water vapour present. If you have some method (regular old air currents work) of removing the vapor over the water, you'll generate more vapor from the remaining liquid to reach an equilibrium. This is why if you leave a glass of water on your kitchen counter, the water will eventualy evaporate.
Try the links in the MadSci Library for more information on Chemistry.