How can I avoid dehydration?

The first step to avoiding dehydration in exercise is to start with a full tank. Drinking 1-2 cups of water in the half hour before exercise is generally enough. Don't force yourself to drink. I general your thirst is your best guide. For those who wish to be more scientific about it, you can find out your own sweat rate for a given temperature and exercise intensity. 

This is how you do it:

1. Weigh yourself (digital scale that goes to the tenth of a pound is best), without clothes (this is important afterwards because clothes can absorb water weight after your exercise).
2. Exercise for an hour at a similar temperature and intensity as your planned activity.
3. Weigh yourself after exercise, sans clothes.
4. Each pound of weight loss equals one pint (2 cups) of fluid.

For example, if you lost one pound in an hour of exercise then that equals 2 cups of fluid. Therefore, you should drink a cup every half hour in your exercise. 

So this gives you how much to drink, but what should you drink?  Well, to understand this we must remember that hydration involves not only water, but electrolytes also. Most important is sodium. I know that everyone talks about potassium, but sodium is the most important in hydration and even in muscle cramping, too. Sports drinks, like the original Gatorade, were developed for a reason-they are based on research. After exercising ½-1 hour electrolyte depletion becomes an issue. Good sports drinks will have sodium chloride as a major ingredient and sugar also, about 15 gm/8 oz. The sugar helps in the absorption of the electrolytes. 

Hydration after exercise is also important, but once again listen to your body (thirst). If you have exercised more than 4 hours, be careful not to drink too much afterwards. This can contribute to low sodium levels, a potential medical emergency.