Caffeine may not be drying you out
Medical experts have been saying for years that caffeine acts as a potent diuretic. Consume too many caffeinated beverages, and you end up drinking yourself into dehydration.
But research has not confirmed that notion. Most studies have found that in moderate amounts, caffeine has only mild diuretic effects - much like water.
Details:
http://www.nytimes.com/2008/03/04/health/nutrition/04real.html?ref=science