What Does Water Do For You? 
Water is an important nutrient for athletes. Water  makes  up  60  percent  of your total body weight and  70  percent of your muscles. Without  enough  water, you can't  work  at  your  top  level  of  performance  and  you  may  even  harm  yourself.
Water  cools  your  body.  As  you  exercise,  your  body   temperature  increased ( even  when  it's  cold  outside ).  As  your temperature increases, you sweat.  When the sweat evaporates from your skin, your body cools down.  
What Happens Without Water?  
Dehydration. If  you  start  exercising  without having enough water in your body, or if you sweat during practice and do not replace the water lost, you may become dehydrated. You can become dehydrated even when you lose just a few pounds as sweat. Once you become dehydrated, you can no longer sweat and get rid of the heat that builds up in your body.
  Dehydration can be dangerous. The first  symptoms  of dehydration include thirst, chills, clammy skin, throbbing heartbeat, and  nausea. When  you  become  more  dehydrated,  you  may  develop  a  headache,  cramps,  and  shortness  of  breath, dizziness, and/or dryness in the mouth.
At  the  most  serious  level  of  dehydration, you can experience hallucinations, deafness, visual problems, swollen tongue, and/or kidney failure.
How Can You Avoid Dehydration?  
* Drink plenty of cool fluids before, during, and after practice and competition. Even if you don't feel thirsty. 
*  Drink 1 to 1 1/2 cups of cool fluid 15 minutes before competition or practice. 
*  Drink 1/2 cup of fluid every 10-15 minutes during the event. 
* Don't rely on thirst alone as a guide to how much water your body needs.
*  Weigh yourself before and after exercising. For every pound lost as sweat,
drink two cups of fluid. 
* Avoid salt tablets. Too much salt increases your body's water needs.
* Salt tablets can also irritate your stomach and cause nausea. 
*  Avoid working out in plastic or rubber suits. They can cause serious
dehydration, limit your performance, and lead to heat exhaustion and heat  stroke.
What Happens If Your Sweat Doesn't Evaporate? 

For your body to cool down, two things must occur. You  must  sweat  and  the  sweat  must  evaporate from your skin. If the sweat doesn't evaporate quickly enough to cool your body down, you can become overheated. This  can  happen  when the weather  is hot and humid or when you are wearing heavy gear.

You  can  avoid  problems  by  following  these  tips  when exercising during hot, humid weather :  

*  Exercise at the coolest time of the day--early morning or late evening.
*   Avoid the middle of the day when the temperature is usually the highest.
*  If you must practice then, build  up  your  tolerance  to heat by working out for a short time each day. Gradually increase  the length of each workout. 
* Wear the lightest clothing and equipment you can. Mesh jerseys, lightweight shorts, and  low-cut socks allow more sweat  to evaporate than sweat suits and heavy gear. 
*  Drink plenty of water before, during, and after practice and competition. 
* When you exercise in cold weather, your body still sweats. To keep warm  and  still  allow  the sweat to evaporate, wear  several layers of loose clothing. Layers of clothing will trap the warmth from your body  while absorbing your sweat. If you  become too warm, a layer can be removed and remember; drink water even in cold weather.

If exercise lasts longer than 60-90 minutes, an athlete may benefit from a sports drink containing a concentration of 8% carbohydrate.  Drinks containing more than 8% (those that tend to be higher in sugar) may cause stomach cramps that can hinder performance.
© 2005-2008. Barrie Spirit Soccer
during or before football matches? Or should you stay to just water?

Water is the best liquid for re-hydrating the body. During exercise, you should ideally consume at least 100-200 grams (6 ounces) each 20 minutes. Unfortunately, when you drink water in large quantities it becomes bland and unappealing. The inviting taste and color of sports drinks stimulate you to drink more. Most sports drinks also provide you with carbohydrates and electrolytes that increase the rate of fluid absorption from the gastrointestinal tract. This gives them a slight edge over water in exercises lasting over one hour.
Make sure you are well hydrated before you start playing or practicing. Drink between 500 grams and 1 liter (up to 24 ounces) two hours prior to kickoff. If you stay hydrated during the exercise you will be fine regardless of whether you're drinking water or Gatorade.
Liquids you should stay away from anything sweetened (including carbonated beverages), juices ...
Is it okay to drink gatorade or    powerade