This quote from benjammin may be the most practical advice on keeping yourself hydrated.

There's been a gradual change in the scientific consensus about how much or how often you need to drink while exerting yourself. In the past, athletes and other active people were advised to "drink as often as you can because thirst is not a good indicator of your water needs". Over the years since then, people have noticed that a lot of people actually suffer from drinking too much water by trying to follow this advice, for example, at marathons. Even sports drinks have a pretty low concentration of electrolytes so if you chug a lot of plain water or even a lot of sports drink, you can still end up with hyponatremia--the excessive dilution of sodium in your body.

Actually, benjammin's observation that you feel sick if you drink more than 2 gal/day, regardless of whether the beverage contains electrolyte, is likely a sign of hyponatremia. There's just too much water entering your body and it's seriously diluting the sodium concentration in your body. Signs of hyponatremia include: nausea, headache, cramps, confusion, slurred speech, bloating and swollen hands. Some of these symptoms are similar to impending heat exhaustion or heat stroke, which makes things confusing because you wonder if you need to drink even MORE water.

USA Track and Field used to advise athletes to drink as much as possible. In 2003, they changed their advice to "drink when thirsty" because of fears of hyponatremia. The International Marathon Medical Directors Association now advises runners to drink ad libitum, that is, at their discretion and not to drink faster than 800 ml/hour (a can of soda is about 350 ml).

Benjammin's observation about Gatorade might be a different phenomenon. Too much sugar inhibits gastric empyting into the small intestine and I have read that Gatorade contains too much sugar, so he may be feeling bloated because the Gatorade stays longer in his stomach than is comfortable. Benjammin, you might try diluting it and see if you still get that bloated feeling.

But benjammin has good advice: listen to your body. To that, I would add: drink when you're thirsty, but don't force yourself to drink more often if you don't feel like it.

In more extreme situations, like if you're really exerting yourself hard, especially in a very hot, dry environment, you may want to push the fluids, though, because you can lose water much faster than you can absorb it and dehydration is a real concern. You can use urine color and weigh yourself to evaluate if you're getting enough or too much water.

Again, I'm not a doctor, so please consult with your own healthcare provider about what's right for your own specific situation.