As Brad said, showers can be good for hydrating, but unless they really need it I would not do it all that often. If you live in an area where you have sunning cages outside you can shower them from the hose but make sure the water in the hose is not too hot (baking in the sun all day) or too cold.
Is there a specific reason you are inquiring? Keep in mind, too that they do not absorb poisture thru their skin as much as thru their nasal passage so humidity is really key.
lele