If you eat a healthy diet, about 20 percent of your water may come from the foods you eat. If you eat a healthy diet you can drink 166 ounces of water today, or 5 liters.
Remember that water is the best source for your daily fluid needs. Other good beverages include milk, herbal teas, low-sodium broth, 100% fruit and vegetable juices. Soft drinks will also count toward your daily total of fluid, just remember that sugar sweetened soft drinks and fruit juices add extra calories to you daily diet that you don't need. I always just try to stick it out with water, unsweet tea and skim milk. Kicking that soda habit or addiction in my case will help you out a lot.
Sources:
CDC: Tips for Preventing Heat-Related Illness. http://www.bt.cdc.gov/disasters/extremeheat/heattips.asp
Dietary Reference Intakes: Water, Potassium, Sodium, Chloride, and Sulfate. http://www.iom.edu/?id=18495&redirect=0.
