Dehydration really affects your performance on the court, both physically and mentally. Most sports drinks combat this with some combination of water, sugar, sodium and electrolytes. The H2O, sodium and electrolytes are there to replace what you lose in perspiration, but the sugar is there primarily to give your muscles a quick meal for energy. But there's a downside: all the sugar is a lot of calories. And that can really counter the exercise effect of a few hours of singles. Glaceau Smartwater is different. This is pure, vapor-distilled water, with added electrolytes like magnesium, calcium and potassium, and nothing else. No salt, no sugar, no weird chemicals. So, when you're in training and need to get maximum evercise benefit, this is the drink for you.