If you’re not guzzling water before, during, and after your workout, you’re hurting yourself in the long run. And the real problem is that most people — including professional athletes — are dehydrated before they even begin a workout. One studyrecently looked at a group of college football players preparing for NFL scouts, and found that 98 percent of them were dehydrated the morning of the evaluation. And when you’re dehydrated, the experts say, your performance during, say, a 10-mile run or a heavy-duty workout, is decreased by 25 percent. So how much water should you be drinking? At least two to two-and-a-half 8-ounce glasses up to two hours before your workout, one 8-ounce glass 15 minutes before, and one 8-ounce glass every 15 minutes during your workout, the experts say. That way, you can fight dehydration and sweat losses early on.