Keeping your water (fluid) intake up while exercising and even during non-exercising periods is critical to your performance in exercise, especially since studies have shown that as little as a 2% drop in your weight due to water loss can dramatically lower your performance level.

Typically the daily recommendation for water intake is to drink about ½ ounce per pound of body weight or about 10-eight ounce glasses if you weigh 160 lbs. If you are working in a stressful (hard work, hot) environment then 2/3 ounce per pound or 13-14 glasses are recommended a day.   

During exercise, studies show that different individuals lose more water faster than others in similar environments (hot, cold, humid, etc.). It is quite individual. So the recommendation for fluid intake during exercise should be determined according to how much water weight you typically lose during your exercise.  If you lose 2 pounds of weight during a 1-hour exercise bout then you should be trying to replace a similar amount during your exercise activities. For each pound of body weight you lose you will want to try to replace it with 16 ounces of water. Use the spreadsheet formulas below to determine your fluid requirements.

Sport drinks are also recommended to help maintain electrolyte (salt) balance and maintain blood glucose levels (for events lasting longer than 1 hour).  Typically, a 5 to 8% solution (carbo/fluid) is recommended.

Keep a look out for Hyponatremia but Keep Drinking Water

Despite the recent warnings in the literature of the possible hazards from drinking too much water, most of us need to drink more. The warnings against excessive drinking were related to research findings on marathon and triathlon participants who suffered water intoxication (hyponatremia) while running in the longer events. Those who suffered from this condition were typically the slower runners who were drinking frequently while at the same time losing exceptionally large amounts of sodium from sweating. Due to the long and strenuous exertion this loss of sodium created a severe imbalance between their hydration level and the electrolyte (sodium) levels causing symptoms such as nausea, fatigue, stupor and even coma and death.  In such severe exertion cases, even sports drinks do not supply enough sodium. One possible remedy to this risk is to eat salty snacks during the race.