Staying hydrated when exercising in hot, humid weather is really important. However, if you are exercising, at a moderate level, for longer than an hour you should probably reach for a sports drink.
Unlike water, sports drinks contain electrolytes and carbohydrates to help your body absorb and retain fluid lost during exercise. Because of this, sports drinks do a better job of preventing dehydration and maintaining proper electrolyte balance, especially in warm, humid conditions when you sweat out more fluid and sodium. Replenishing sodium enhances fluid absorption and retention and prevents hyponatremia, the condition when blood sodium blood levels fall below normal, which in extreme cases can be fatal.
Look for a sports drink that contains at least 500 to 700 milligrams (mg) of sodium per liter. Also select one you don't feel like you need to dilute due to taste, since you'll dilute the electrolyte and carbohydrate concentration as well. To avoid guzzling too much at one time since no one likes to run with a belly full of liquid, drink it in small amounts at regular intervals, every 15 to 20 minutes.
Fit's Tip: To figure out how much you need to drink, weigh yourself naked before and after a typical hour of working out. Then drink the same amount you lost. For example, if you lose two pounds during one hour of running, you need to replace about 32 ounces (two pounds) of fluid during each hour of exercise. This is the equation you should use if you are racing too. If you're consuming more than that, you're probably over-hydrating.