More for the parents of athletic children, this article from The New York Times‘ Well blog still contains some useful all-round advice on hydration during exercise. In the comments the author also links to this urine colour test for dehydration.

When [exercising children] were offered grape-flavored water, they voluntarily drank 44.5 percent more than when the water was unflavored. And when the drink included 6 percent carbohydrates and electrolytes — when, in other words, it was a sports drink — they eagerly downed 91 percent more than when offered water alone. Does this mean that parents […] should be stocking their refrigerators with [sports drinks]? The answer is a qualified ‘yes.’ […]

But that ‘yes’ has clear and definable limits. ”Sports drinks are only appropriate in the context of sports, and I mean serious sports,” emphasizes Nancy Clark, a registered dietician and sports nutritionist in Boston, who often works with young athletes. If, however, your 12-year-old or older athlete has begun competing at a more intense level, especially if he or she participates in multiple practices or competitions in a single day during the summer, “sports drinks are appropriate,” Clark says.

So not you or I after our daily workout, basically. The article also contains this recipe for making your own sports drink:

1/4 cup sugar
1/4 teaspoon salt
1/4 cup hot water
1/4 cup orange juice
2 tablespoons lemon juice
3 1/2 cups cold water

(Dissolve the sugar and salt in the hot water then add the remaining ingredients. Approx. 50 calories and 110 mg of sodium per 8 ounces.)

via Lifehacker