FORGET FOR a moment the fact that severe dehydration can result in kidney and heart failurehell, even high-school football coaches know that. (We hope.) Just a slight dip in your body's H2O reservoir can diminish coordination, reduce mental acuity, and provoke overheating; more simply, dehydration makes you stumble around like an idiot before you ultimately bonk and drive your face into the gravel. For top-flight athletes, this can mean the difference between a cash purse and a DNF; but for the rest of us, whether we're balancing a mountain bike on an off-camber trail crawling with wet roots, or limping to the finish of that first ultra run, a mouthful of cool water can better the odds of success. Bicyclists, of course, have known the benefits of no-hands drinking for years, but pack manufacturers have recently begun producing hydration systems that let you gulp on the run regardless of your sport. Here are our top selections for getting over that drinking problem of yours. Cheers.