Perspiration is the body's way of staying cool, but that moisture loss has to be replenished regularly. If you're physically active on a hot day, drinking four 16- to 32-ounce glasses of liquid an hour isn't too much. This is true even if you're not thirsty, so drink up.
For hydration, all beverages aren't created equal. Avoid alcoholic beverages, even beer. You should also steer clear of beverages that are high in sugars. These false friends can actually cause you to lose more fluid than you gain. Another smart move is to drink your beverages cool but not ice cold. Very cold drinks can cause stomach cramps.