A: Drinking to quench thirst isn't enough. You need to drink past thirst. Studies have shown that drinking to satisfy thirst only replenishes two- thirds of the amount of water a person should drink when working or playing in the Arizona sun. Through perspiration, a person can lose about two quarts of water an hour. To replace that loss drink about a glass of water every 10 minutes. That's a significant amount of fluid.

One way to tell if you're properly hydrated is urine output. If you urinate your normal amount and frequency, the body is well-hydrated, provided you don't have kidney disease. I think that's a better gauge than how thirsty you feel.

And what a person drinks may make a difference. In the long run, whether drinking a sports drink or just water the primary issue still is hydration. In general, it's better to drink plain water than any other fluid, like a sports drink. Sweat contains far more water than electrolytes, which many sports drinks contain. But if you lose a lot of sweat for hours then you'll need to replace the electrolyte solutions as well.

Harvey Meislin, M.D., director, Arizona Emergency Medicine Research Center at The University of Arizona College of Medicine in Tucson

For referral to a UA physician, please call University Health Connection. (520) 694-8888.

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