In addition, drinking water before and during exercise can enhance your athletic performance. Thirst alone is not a good indicator of how much you need to drink, because your thirst is quickly depressed by drinking very small amounts of water. Bring a water bottle with you when you exercise so that you can replace your fluids while they're being depleted. Drinks that contain caffeine are diuretics, increasing dehydration. They can also cause the jitters and shakes.
Alcohol is also a diuretic.
In addition, it is a poor energy source, and can depress the heart and nervous system. Advertisements would like us to believe that a great deal of sodium and potassium is lost through regular exercise. This is not true for a normal workout, like an aerobics class. One study on triathletes showed that only a very, very small amount of potassium is lost, even in such a grueling event. If you do like the taste of the carbohydrate-based sports drinks, dilute them, and you'll save a bit of money and still replenish your fluids effectively for your average workout.