You need to take in about two quarts of fluid a day. That's 64 ounces, or the equivalent of eight 8-ounce glasses of water. Drinking water is the best way to stay hydrated. However, coffee, tea, juice, soup, and other beverages also count. Try not to get your fluids from sugary soda or other high-calorie beverages.
The amount of moisture outside your body is also important.
Is the weather dry where you live?