caffeine boost still counts toward your hydration goal. After all, it's basically water, unless you muck it up with flavored syrups or dairy. "Caffeinated beverages do not dehydrate you when consumed in moderation, that is, five cups or less per day of coffee, tea, or cola," says Lawrence Armstrong, Ph.D., professor of kinesiology at the University of Connecticut and author of Performing in Extreme Environments. In fact, Dr. Armstrong says that any fluids you ingest will help keep your cells saturated, including juice, iced tea, or soda. (Just keep an eye on the calorie count in order to wet your whistle without widening your waistline.)