Remember those westerns, where Rowdy Sixgun loses his trusty mount and has to hoof it across the desert? Recall his parched lips, hangdog gaze and wobbly walk? That's how it feels to bicycle in the hot summer sun if you make the mistake of not drinking enough water. At first, you feel cool because you generate a breeze pedaling along. Forget to drink, though, and the sun's rays and your efforts leave you salt stained, rubbery legged and barely able to balance.