Hydration is one of my favorite topics when working with athletes. The athletes that even take an interest in their diet can sometimes forget the impact that water has on their performance. From what I have seen, I believe that the general public knows that they need to stay hydrated by drinking water throughout the day, but just does not understand proper hydration habits. Most clients have been surprised when I calculate their daily water requirements and see how much they actually need. I am also shocked when I find out that the average person does not know how much 8 oz of water is.
During and after training we have dehydration ques, like feeling thirsty or darker colored urine, to let us know that we need water. During and after training our temperature is elevated, which through sweat we cool our body. Feeling warm and sweaty is also a mental trigger to drink more water because we are losing water. In adult athletes, a loss of 2% of body weight due to dehydration has been shown to have negative effects on performance. In children, the negative effects of fluid loss begin to occur at only a 1% decrease in body weight.
A brochure from the American College of Sports Medicine recommends drinking between 3-8 ounces of water every 15-20 minutes when exercising for less than 60 minutes and drinking 3-8 fluid ounces of a sports beverage that is 5-8 percent carbohydrate with electrolytes every 15-20 minutes when exercising more than 60 minutes. They also mention not to drink more than one quart of water per hour during exercise.
For my high school rowers, I generally recommend up to 34 to 50 oz per hour to minimize sweat-induced body-water deficits during exercise as long as pre-activity hydration status is good. Pre- and post-activity body weight measurements can provide more information for individual rehydration needs, but I don’t usually take the time to do that for each of my athletes unless there is a real concern. I will recommend electrolyte-supplemented beverages that emphasize sodium for workouts lasting longer than one hour or in hot weather.
Before training we do not have these same ques to remind us to hydrate. Thirst is not the best indicator of dehydration. You may not feel thirsty before you're training but this is an equally important period to be hydrate.
I have seen that there is a true lack of education on hydration. People understand that they need water, but do not know how much. I often get the question of what other drinks count as water, and without rolling my eyes I have to explain to them that water counts as water.
Council on Sports Medicine and Fitness and Council on School Health, Bergeron MF, Devore C, Rice SG; American Academy of Pediatrics. Policy statement — climatic heat stress and exercising children and adolescents. Pediatrics. 2011;128(3):e741-e747.