http://www.clevelandclinic.org/healthextra/default.asp?index=9013
Warm weather brings with it thoughts of cool ocean breezes, napping in the hammock, and sipping a tall glass of lemonade. Now hold on to the mental image of that lemonade. Because summer is also a time to be wary of dehydration: the lack of sufficient water in the body.Water is important to the body at all times, but especially in warm weather. It keeps the body from overheating. When you exercise, your muscles generate heat. To keep from burning up, your body needs to get rid of that heat. The main way the body discards heat in warm weather is through sweat. As sweat evaporates, it cools the tissues beneath. Lots of sweating reduces the body's water level, and this loss of fluid affects normal body functions.
What are the signs of dehydration? They include fatigue, loss of appetite, flushed skin, heat intolerance, light-headedness, dark-colored urine, or a dry cough. If you suspect that someone is dehydrated, seek immediate medical attention.
The best way to beat dehydration is to drink before you get thirsty. If you wait until after you're thirsty, you're already dehydrated. To avoid dehydration, active people should drink at least two cups (16 ounces) of fluid one to two hours before an outdoor activity. After that, you should consume five to ten ounces of fluid every 10 to 15 minutes that you are outside. When you are finished with the activity, you should drink some more. How much more? To replace what you have lost: at least another two cups.
One way to make sure you are properly hydrated is to check your urine. If it's clear, pale or straw-colored, it's okay. If it's darker than that, keep drinking!
Some beverages are better than others at preventing dehydration. Water is all you need if you are planning to be active for only an hour or less. If you plan to be exercising longer than that, or if you anticipate being out in the sun for more than a few hours, you may want to hydrate with some kind of sports drink. These replace not only fluid, but also chemicals like sodium and potassium, which are lost through perspiration. Too much or too little sodium and potassium in the body can cause trouble.
Alcoholic and caffeinated beverages, such as coffee, teas and colas, are not recommended for optimal hydration. These fluids tend to pull water from the body and promote dehydration. Fruit juice and fruit drinks may have too many carbohydrates, too little sodium, and may upset the stomach. If you're going to drink fruit juices while exercising, you may try diluting them with water first.
Adequate hydration will keep your summer activities safer and much more enjoyable. If you need to increase your fluid intake, keep an extra pitcher of cold lemonade in the refrigerator.