Every training athlete should drink about 0.5 – 1.0 ounces of water per day per body pound. During training, hydration is of paramount performance. You need to have proper hydration intake to keep your body moving and nutrients to where they need to be. Muscle tissue is 70% water and needs it to create ATP (energy).
Race day? Believe it or not, 13% of marathon runners suffer from hyponatremia, an overdose of water. To avoid the effects of taking in too much water on race day, assess during training your sweat level. If you are sweating profusely after a short amount of time then you could be drinking too much. Try to reduce the ridiculous amount of sugars in sports drinks by a 50/50 split water ratio. Use electrolytes either added to water or add water to sports drinks to ensure proper amount.