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Have you ever wondered how many glasses of water you should drink a day?


Ali Mollenhauer 



If you are one of the many Americans obsessed with being healthy and slim, you probably try to drink eight glasses of water each day.  You force yourself to keep drinking because it will help you lose weight and, after all, it’s necessary.  But according to whom?  Why have we always believed that we need eight glasses of water daily to keep a balanced diet?  Why is drinking excessive amounts of water such an integral part of our life?  In our society, it is acceptable to drink water anywhere, anytime.  One southern California university even has a pamphlet that encourages its students to “carry a water bottle with you.  Drink often while sitting in class…”  Why are we so obsessed with drinking extreme amounts of water?  Here’s why: We have always been told by doctors, nutritionists, and the media that we need a lot of water in order to stay healthy, balanced, and even slim.  New research, however, suggests that this claim has no scientific foundation.  It is merely a myth that has evolved and escalated over time.  However, it is true that we need close to eight cups of fluid daily, but this does not necessarily mean that it has to be from drinking eight glasses of water.  The recommended eight glasses includes beverages, food, and digestive juices.  According to a study at Purdue University, forty percent of water needs comes from food, and ten percent from body processes. (


How did the myth that we need to drink 8 glasses of water a day start?

It is unclear exactly how this myth started.  A lot of scientists agree that eight glasses of fluid a day are perfectly healthy, but nutritionists admit that they cannot find a study that specifies that number.  Says Professor Barbara Rolls, a Penn State University Nutritionist, “for scientists, to have to admit they don’t know the origin of something is very frustrating”.  Nevertheless, for years magazines, websites, and commercials have been telling people to drink up.  Not surprisingly, bottled water is the fastest-growing drink in America.  By 2005, analysts predict that bottled water will be outselling coffee or milk.  Anything that’s good for us is even better for the industry. (    

Paul Thomas of the National Academy of Sciences in Washington had the best explanation for the origin of the myth.  The academy’s Food and Nutrition Board publishes the United States recommended daily allowances.  In the first edition, in 1943, there was no mention of water.  The next edition, in 1945, however, read, “A suitable allowance of water for adults is 2.5 liters daily in most instances.  An ordinary standard for diverse people is 1 milliliter for each calorie of food.  Most of this quantity is contained in prepared foods”.  Somehow, this last sentence was disregarded.  Furthermore, Dr. Erwin Stillman’s publication in 1967, the Doctors Quick Weight Loss Diet, also contributed to the eight-a-day hysteria.  His book sold more than 12 million copies.  (

Physician Heinz Valtin, of Dartmouth Medical School, also sought to find the origin of this myth and to examine scientific evidence, if any, that might support it.  Valtin is a kidney specialist and author of two widely used textbooks on kidney and water balance.  He strongly doubts the validity of the myth that we need to drink eight glasses of water a day.  Rather, he finds it “difficult to believe that evolution left us with a chronic water deficit that needs to be compensated by forcing high fluid intake”. (  

So how much is enough?

According to the doctors of Harvard Medical School, we lose about 2.5 quarts of water (ten 8-ounce glasses) through sweat, exhaled air, urine, and feces on most days.  To replace it, the National Research Council recommends consuming about 1 milliliter of water for every calorie you burn.  For example, if you burn 2,000 calories a day, you will need a total of 2,000 ml of water, which is equivalent to two quarts.  Since it is hard to estimate how many calories you burn, there is a simpler method of figuring out the approximate number of ounces of water you need each day – just divide your weight by two.  (


 Is the amount of water one should drink the same for everyone?

No. The overweight person needs one additional glass for every 25 pounds of excess weight.  The amount one drinks should be increased also if the weather is hot and dry or if one is doing a lot of exercising.  Water should preferably be cold.  Cold water is absorbed more quickly than warm water.  Some evidence suggests that drinking cold water can actually help burn calories.  (


What about older people?  Don’t they need more water than the rest of us?

Experts have always warned that older people are especially prone to dehydration because they have lost their sense of thirst.  New research, however, suggests that this may be an overstatement.  According to a report in the July 2000 Journal of Gerontology, Robert Lindeman, MD, surveyed fluid consumption among 833 elderly volunteers.  He found that “people who drank less than four glasses of water a day were no more likely to show signs of dehydration than those who drank six or more”.  When looking at the standard markers for dehydration, Lindeman found no difference between those who drank a little water and those who drank a lot.  (   

What claims are made about the purposes of drinking a lot of water?

Up to 60% of the human body is water.  The brain is composed of about 70% water, blood is 82% water, and the lungs are nearly 90% water.  Water is the principle constituent of the fluids that surround and are within all living cells.  Only oxygen is more important than water for sustaining life.  Experts say there are many health benefits for those who drink sufficient amounts of water daily.  Water is vital in maintaining and regulating the body’s systems.  It lubricates joints and organs, maintains muscle tone, keeps skin soft, regulates body temperature, filters out impurities, and keeps our minds alert. (


What are some benefits of drinking a lot of water?

Michael Manning, M.D., of Allergy and Immunology Associates in Scottsdale, Arizona, believes that water is essential when coping with allergies.  It keeps the secretions thin, allowing them to flow easier through the sinus passages.  Water has also been proven to have particular health benefits for women.  An experiment conducted at the Fred Hutchinson Cancer Center in Seattle found that among women who drank more than five glasses of water daily, there were fewer cases of colon cancer.  The risk was about half of what it was for women who drank less than two glasses a day.  In addition, drinking eight to ten glasses of water a day has been proven to reduce the incidence of urinary tract infections in women.  By increasing the amount of fluids excreted from the body, more bacteria is flushed that could lead to infection. (

Also, according to a study published in the New England Journal of Medicine, Dominique Michaud found that a high fluid intake is associated with a decreased risk of bladder cancer in men.  (Michaud, 1999)  In addition, water helps flush waste out of the body.  This is important in weight loss because during weight loss the body has a lot of waste to get rid of – all of the metabolized fat must be shed.  Water can also help relieve constipation.  The colon is a primary internal water source, and when the body gets too little water it needs to take some from its internal source.  The result is constipation.  Once the body is re-hydrated, normal bowel function can return.  (


What happens when the body becomes dehydrated?

The body needs so much water a day because it does not have a reserve of water.  Once the body runs out of its water supply it cannot re-hydrate itself.  When the body becomes dehydrated, the signs are both mental and physical.  The symptoms of dehydration include light-headedness, dizziness, nausea, thirst, and fatigue.  A water deficit of only one quart of water slows blood circulation and reduces concentration. (

 According to Kari-Ann Harrison, Products Specialist, in 37% of Americans, the thirst mechanism is so weak that it is often confused with hunger. 75% of Americans are chronically dehydrated.  Mild dehydration will slow down one’s metabolism as much as 3%.  (

When a body is dehydrated, it pulls water from a lot of different places in the body to compensate for the lack of water.  Water is taken mostly from inside one’s cells.  Some water is taken from outside the body cells, and 8% is taken from blood volume.  This causes one’s body to close some capillaries, making blood thicker and harder to pump around the body.  This has implications in hypertension, high cholesterol, and heart disease.  Lack of water is also linked to, and currently being studied for, its role in headaches, arthritis, and heartburn. (   


Is it possible to drink too much water?

According to Heinz Valtin, yes!  Valtin claims that even modest increases in fluid intake can result in “water intoxication”.  This occurs when one’s kidneys are unable to excrete enough water.  Although it may seem unlikely for this to occur, such instances are not unheard of.  Water intoxication has led to mental confusion and death in athletes, in teenagers after ingesting the drug ecstasy, and in ordinary patients.  Other disadvantages of a high water intake include: possible exposure to pollutants, frequent urination, expense for those who choose to drink bottled water, and feelings of guilt for those who have not met the “8 X 8” requirement, as Valtin calls it. (      


Not everything we believe is backed by scientific evidence.

We are always told that by the time we are thirsty, we are already dehydrated.  This may apply in certain instances.  For example, studies of marathon runners and military recruits in training have found that some people focus so intently on their exercise that they block thirst sensations until they’re in trouble.  However, Barbara Rolls, a Pennsylvania State University expert on thirst, did hourly hydration tests to prove that drinking when thirsty is good advice for the rest of us. (  In 1984, Rolls and a group of colleagues at Oxford University followed a group of men as they went through their daily routine.  They found that the volunteers became thirsty and drank long before their hydration levels showed any signs of dropping.  (

Another common misconception that we have always believed is that dark urine means dehydration.  According to Valtin, at normal urinary volume and color, the concentration of blood is within the normal range and nowhere near the values that are seen in true dehydration.  Therefore, the warning that dark urine signifies dehydration is false in most instances. (


Does drinking a lot of water really contribute to weight loss?

Unfortunately, this is another myth.  Drinking a glass of water doesn’t do anything to take the edge off hunger.  Barbara Rolls says, “Water sneaks right past without triggering satiety signals, the cues that tell your body when you’re full”.  However, there is some hope for all of you dieters out there.  Adding water to the food you eat does seem to tame hunger.  In a study reported in the October 1999 American Journal of Clinical Nutrition, Rolls found that women who eat a bowl of chicken soup feel fuller than those who eat chicken casserole served with a glass of water, even though both of the meals contained exactly the same ingredients.  The soup eaters also tended to be less hungry at their next meal and consumed fewer calories than those who ate the casserole. (


What about soda, fruit drinks, and coffee? Are they really so bad after all?

The consumption of these drinks is a topic of controversy.  Many experts say that carbonation interferes with fluid absorption, and caffeinated beverages don’t help because they accelerate water loss through urine.  (

However, according to Elizabeth Cohen of CNN news, several experts with whom she consulted said that when they look at several studies, people get just as hydrated from caffeinated beverages as they do from decaffeinated beverages.  Obviously, drinking only caffeinated beverages all day would not be very beneficial, but if you have a cup of coffee in the morning and a cup of tea at night, you can count that toward your water intake. Cohen says you can get your water from a number of other beverages as well. Milk, for example, is 84% water.  Diet coke is 99% water. (  University of Nebraska researcher, Ann Grandjean, published a study in the Journal of American College of Nutrition about the effects of caffeinated beverages on hydration.  Grandjean and her colleagues used 18 healthy male adults for their subjects.  On four separate occasions, the males consumed water or water plus varying combinations of beverages.  The beverages were carbonated, caffeinated, caloric and non-caloric colas and coffee.  Body weight, urine, and blood evaluations were performed before and after each treatment.  Grandjean found that there were no changes in the body weight, urine, or blood evaluations for the different treatments.  The study found no significant differences in the effect of various combinations of beverages on hydration status of healthy adult males.  Therefore, Grandjean concluded that advising people to disregard caffeinated beverages as part of their daily fluid intake is not supported by the results of her study. (Grandjean, 2000)  


A closer look…

We absorb a lot of water from the foods we eat.  Fruits and vegetables are 80 to 95 percent water.  Meats contain an adequate amount, and dry bread and cheese are about 35 percent water. (  

Below is a chart that was adapted from the 17th edition of Bowes and Church’s Food Values of Portions Commonly Used.


Water content of some foods

Food/serving size              Water content (oz)

Yogurt 1 cup                           5.8

Watermelon 1 cup                  5

Pineapple 1 cup                      4.5

Strawberries 1 cup                 4.5

Apple 1 medium                     4

Asparagus 6 spears

(cooked)                                  3

Banana 1 medium                  2.8

Spinach ˝ cup cooked           2.8

Lettuce 3 leaves                     2.7

Broccoli ˝ cup boiled             2.5



In the meantime…

We really do not know for certain exactly how much water we need!  We can be pretty certain, however, that we do not need to drink eight glasses of water a day.  The best suggestion I have gathered is to simply drink when you feel thirsty.  If you start to get a headache or a dry mouth, you know you are not drinking enough.  Furthermore, it seems rather safe to conclude that drinks like soda, fruit drinks, tea, and coffee can be counted toward your water intake.  Fortunately, The National Academy of Sciences has put together a panel of experts to do nothing except look at how much water we need.  Hopefully, in March they will have an answer.  The Institute of Medicine is also reviewing research on how much water we need.  They will issue a report next spring as well.


Who is presenting this information, and why are they presenting it?

This information is being presented by a variety of people.  Most of the information has come from professors and doctors of renowned universities across the nation.  The people that have been cited on this website spend the majority of their career researching health issues such as the effects, benefits, and necessity of water.  Once they have reached a conclusion from their research, they publish it and present it to the rest of society so that we may share and benefit from their knowledge.    




▫ The AFU and Urban Legend Archive Medical. “Eight glasses of water”. 1994. September 11, 2002.


▫ CNN news. “How much water do we really need?” August 20, 2002. pgs.1-3. September 11, 2002.


▫ Cohen, Elizabeth.  “How much water do we really need?”. May 24, 2002. pgs. 1-3. September 11, 2002.


▫ Dartmouth Medical School Communications. “Drink at least 8 glasses of water a day – Really? Dartmouth Professor Finds no Scientific Evidence For 8 X 8”. August 8, 2002. pgs. 1-3. September 11, 2002.


▫ Grandjean, Ann; Reimers, Kristin; Bannick, Karen; Haven, Mary. “The Effect of Caffeinated, Non-caffeinated, Caloric and Non-Caloric Beverages on Hydration”. Journal of the American College of Nutrition. 2000. Volume 19: 591-600. Number 5.


▫ Harrison, Kari-Ann. “Why your body is trying to tell you it needs water!”. September 19, 2002.


▫ Harvard Health Online. “How much water do you need?”. September 2002. pgs. 1-3. October 4, 2002.


Jaret, Peter. “Water, water, everywhere. But how much do you really need to drink?”. April 16, 2001.  pgs. 1-3.  October 11, 2002.


▫ Komo Staff & News Services. “The Myth Behind 8 Glasses of Water A Day”.  May 23, 2002. September 11, 2002.


▫ Michaud, Dominique; Spiegelman, Donna; Clinton, Steven; et al. “Fluid Intake and the Risk of Bladder Cancer in Men”. The New England Journal of Medicine. May 6, 1999. Volume 340:1390-1397.  Number 18.


▫ Musk, Maye. “Water – the myth of 8 glasses”.  Pgs. 1-2. October 10, 2002.   


▫ Palumbo, Christine. “Good Health Begins With Water”. 2002. September 19, 2002.


▫ Smith, Martin. “Six Glasses Of Water A Day Can Keep The Doc Away”. 1996. September 19, 2002.



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