By Martha A. Simpson, D.O., M.B.A.
Associate Professor of Family Medicine
Ohio University College of Osteopathic Medicine

EIGHT GLASSES OF WATER A DAY IS A GOOD RULE OF THUMB

Question: How much water intake is most appropriate? Is it "the more the better"? Or is there any specific amount of water that's good for everyone? Or is it just depending on each person's individual needs?

Answer: You have asked a lot of interesting questions. I’ll try to answer them as best I can. The knee-jerk response to “how much water should an adult drink a day” is eight eight-ounce glasses a day or 64 ounces. This is not a bad rule of thumb but water intake is unique to each person and his or her situation.

Water is vital to human existence and people can live for quite a while on just water -- I do not recommend this!!! To be more specific, the amount of water you need is based on body size, age, basic medical status, activity level and environment.

Many experts suggest that you should drink half of your body weight per day in ounces of water. Therefore, if you weigh 150 pounds, you should drink 75 ounces -- or slight more than nine glasses -- of water each day. This only assumes that you are not obese. If you weigh 350 pounds, it would not be appropriate to drink 175 ounces of water daily. Conversely, if you weigh 100 pounds and are 5 feet 6 inches tall, you are severely underweight and probably need more that 50 ounces of water per day. So this method works primarily for people with a body mass index (BMI) between 18 and 25. You can calculate your BMI at: www.cdc.gov/nccdphp/dnpa/bmi/

If you exercise enough to break a sweat, you should add about 20 ounces of water to the daily intake to balance out your perspiration loss. People who exercise in a very warm environment need to add even more to replace their exercise loss. In general, people who live in very hot and dry climates, need more water than those who don’t.

Now, this may sound like a lot of water. Most Americans probably don’t drink as much water as they should. You may be relieved, however, to learn that you can count servings of fruits and vegetables toward your target number of glasses per day. That is, five large servings of fruits and vegetables could count as a glass or two toward your daily goal. Remember that water constitutes about 90 percent of most fruits and vegetables.

On the down side, if you consume caffeinated drinks such as coffee and many soft drinks, or alcoholic beverages, you may need to add additional water consumption to your daily routine. This is because these beverages have a diuretic effect.

You can drink too much water and cause a very serious medical condition called water intoxication. This occurs when you take in enough water to create an imbalance in your electrolytes. That can lead to death if not promptly identified and corrected. So more water is not always better.

A final note, what I’ve said here is based on the general consensus of experts. However, in truth, there’s not been a lot of good scientific study on this subject. I suggest that my patients drink enough water so that they urinate 4 to 6 times during the day -- again assuming they are healthy adults.

Family Medicine® is a weekly column. To submit questions, write to Martha A. Simpson, D.O., M.B.A., Ohio University College of Osteopathic Medicine, P.O. Box 110, Athens, Ohio 45701, or via e-mail to readerquestions@familymedicinenews.org. Medical information in this column is provided as an educational service only. It does not replace the judgment of your personal physician, who should be relied on to diagnose and recommend treatment for any medical conditions. Past columns are available online at www.familymedicinenews.org.