The amount of water you need to be adequately hydrated varies depending on your, body weight, body temperature, duration and intensity of exercise, and many other contributing factors. We offer this simple hydration tool that will calculate a recommended water intake guideline that will support your hydration needs.
*The Hydration Calculator provides an estimate of the quantity of water you need to consume in one day based on your weight and activity level and is not intended to give precise amounts.
When exercising vigorously, you need to begin in a well hydrated state. Therefore, the National Association of Athletic Trainers (NATA) recommends that you drink 17 to 20 ounces of water 2 to 3 hours before exercising and 7 to 10 ounces, 10 to 20 minutes before exercising. In addition, NATA suggests a range of 7 to 10 ounces of water every 10 to 20 minutes during vigorous exercise. However, the best way to tell if you are drinking enough water during exercise is to weigh yourself before and after exercising. A one pound weight loss is equivalent to 16 ounces of water.
Excessive fluid consumption can result in hyponatremia, a dangerous condition that may arise when endurance athletes drink too much water or other fluids during extended strenuous exercise, thereby diluting the body's sodium levels.
The symptoms of hyponatremia include bloating and puffiness in the face and fingers, nausea, vomiting, muscle weakness, headache and disorientation. It any of these symptoms occur during exercise, seek medical attention immediately. (source http://www.bottledwater.org)