In 1945 it was determined that the average sedentary adult needs approximately 64 ounces (oz.) of fluid daily, which is probably where the proverbial "8 glasses of water daily" recommendation came from (8 x 8 oz. = 64 oz.). What's missing is that the 64 oz. is from all sources including food, coffee, tea, diet drinks, etc., and contrary to popular belief, all the drinks mentioned contribute to your total fluid intake equally. In other words, none are significantly more diuretic than another according to all studies. The good news is that your thirst will tell you when you need fluid, but athletes and older adults need to pay greater attention as listed below.
Current fluid requirements for healthy sedentary adults living in temperate climates are as follows: Men 125 oz. (~3 qts) of water per day from all dietary sources; Women 91 oz. (~2 qts) of water per day from all dietary sources. Approximately 20% of your fluid requirements will come from the food you eat. Below are the guidelines for athletes and exercisers:
Pre-exercise Guidelines
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Drink approximately 16 to 24 ounces of fluid two hours before activity.
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On warm or humid days, drink an additional eight to 16 ounces 30 to 60 minutes before activity.
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Water is adequate for activities less than an hour as long as meals are consumed regularly.
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For endurance events, training sessions longer than 60 minutes, or multiple practices a day, choose a sport drink containing four to eight percent carbohydrate (e.g. Gatorade).
During Exercise
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Depending on your sport, consume three to six fluid ounces of water or sports drink every 15 minutes. This equates to approximately 32 ounces per hour.
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For prolonged exercise greater than 60 minutes, choose a sports drink with small amounts of electrolytes.
Post-exercise Guidelines
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Immediately following activity, drink at least 16 to 20 ounces of fluid for every pound of weight lost to ensure proper rehydration.
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A liquid shake with high carbohydrate content, minimal protein and fat can refuel energy stores and maximize recovery after demanding training bouts. Consume this as soon as possible after workouts or events. The dotFIT FirstString™ Powder meets the NCAA guidelines and is ideal for youth and college athletes.
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Drink an additional 16 ounces with your post workout meal. This meal should be consumed within two hours after activity.
If necessary weigh yourself each morning. A fairly stable weight generally indicates proper fluid balance.