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. For referral to a UA physician, please call University Health Connection.