To get an idea of just how much you need to drink, weigh yourself before and after your workouts. Any weight decrease is probably due to water loss. Any weight gain could indicate you are drinking too much.
Sports drinks can be helpful to athletes who are exercising at a high intensity for 60 minutes or more. Fluids supplying 60 to 100 calories per 8 ounces helps to supply the needed calories required for continuous performance. It's really not necessary to replace losses of sodium, potassium and other electrolytes during exercise since you're unlikely to deplete your body's stores of these minerals during normal training.
If, however, you find yourself exercising in extreme conditions over 3 or 5 hours you will need to add a complex sports drink with electrolytes. Athletes who don't consume electrolytes under these conditions risk overhydration or hyponatremia. The most likely occurence is found in the longer events (five hours or more) when athletes drink excessive amounts of electrolyte free water, and develop hyponatremia (low blood sodium concentration).
While caffeine may have some ergogenic properties, remember that it acts as a diuretic causing your body to excrete fluid instead of retaining it, so it is not the wisest choice when trying to hydrate. You're better off with plain water or fruit juice until your weight reaches that of your pre-exercise state.
Tips for Athletes
If you're exercising intensively in the morning, a sports drink may be better than being on empty. Most people find they do better if they have something, but it can be solid or liquid form.
While you're exercising:
Thirst is not a good indicator at all
If you're thirsty, you're already dehydrated.
Drink something every 15 to 20 minutes, if possible. Since that's not possible in all sports, you may have to drink more before you exercise, so you have enough in your body. Don't try something new before competition: That's a recipe for disaster. The body needs to get used to new fluids, so do it gradually.
Don't drink sports drinks when during off hours - extra calories!
Don't drink fruit juices before exercise: They're a very, very concentrated form of carbohydrate. That means you might get an upset stomach or a laxative effect.
The Dangers of Too Much Water
Hyponatremia, also called water intoxication, is generally the result
of drinking excessive amounts of plain water which causes a low
concentration of sodium in the blood. Once a rare occurrence at
sporting events, it is becoming more prevalent as participation
increases and more novice exercisers are entering endurance events.
There is a disorder called hyponatremia, which means "low sodium.This occurs when someone drinks enormous amounts of water and/or loses too much salt from the body in a short time.
Drinking an enormous amount of water overwhelms the kidneys and they can't process and eliminate the water fast enough, so the amount of sodium in your blood drops too low.
Brain needs sodium and when the sodium levels drop this low a person feels confusion and lethargy.
Severe hyponatremia can lead to twitching, seizures and even death.
Hyponatremia can happen to a marathon runner who drinks gallons of water and doesn't replace the electrolytes during a race, or to people with certain psychological disorders who can't make themselves stop drinking water.
Hyponatremia can also occur in older people and people with certain medical conditions. Hyponatremia won't happen to a healthy person who spreads out his or her water intake over the course of the day. This means it is fine to drink two gallons of water over 16 hours, but drinking two gallons of water all in one sitting can be very bad.
"To the people of poor nations, we
pledge to work alongside you to make
your farms flourish and LetCleanWatersFlow, to nourish starved
bodies and feed hungry minds. And to those nations like ours that enjoy
relative plenty, we say we can no longer afford indifference to
suffering outside our borders; nor can we consume the world's resources
without regard to effect. For the world has changed, and we must change
with it". Source: President Obama, Inaugural Speech, January 20, 2009, Washington, DC, USA.