As physicians know, the Internet can be a powerful educational tool, or it can be the source for disseminating misinformation.

Mass e-mails, the kind helpfully passed from friend to friend to friends of friends ad infinitum throughout cyberspace, are one of the prime culprits when it comes to spreading misinformation passed off and accepted as fact. Case in point: A recent, widely circulated e-mail extolling the virtues of drinking water and rattling off various "facts" concerning underhydration and the inherent dangers of not drinking enough fluids.

Within reason, an e-mail encouraging people to drink more water is a reasonable message.

"That''s a good thing for almost everyone, to be taking in more fluids," said Natalie Allen, a registered dietitian with Barnes-Jewish Hospital in St Louis. "It''s not going to hurt people to drink more water."

Doctors generally agree that drinking an adequate amount of water should be encouraged. But too much of a good thing can lead to hyponatremia, the dangerous and potentially fatal dilution of the blood''s sodium levels—caused by drinking too much water. This is particularly a risk for endurance athletes—runners, triathletes and bicyclists—involved in exertion exceeding 4 hours.

"There have been several deaths over the years in marathoning that have been thought to be attributable to hyponatremia," said Dr Fred Williams, a gastroenterologist at St John''s Mercy Medical Center in St Louis and a veteran marathon runner.

In addition, the recent case of the woman who died from what was termed "water intoxication" after drinking an estimated 2 gallons of water during a radio contest illustrates water consumption can be overdone.

Here are the "facts," all of which lack verifiable attribution, included in the ubiquitous "drink more water" e-mail:

"Fact" 1. Seventy-five percent of Americans are chronically dehydrated (likely applies to half the world''s population).

"Fact" 2. In 37% of Americans, the thirst mechanism is so weak it is mistaken for hunger.

"Fact" 3. Even mild dehydration will slow down one''s metabolism as much as 3%.

"Fact" 4. One glass of water shut down midnight hunger pangs for almost 100% of the dieters studied in a University of Washington study.

"Fact" 5. Lack of water is the No. 1 trigger of daytime fatigue.

"Fact" 6. Preliminary research indicates 8 to 10 glasses of water a day could significantly ease back and joint pain for up to 80% of sufferers.

"Fact" 7. A mere 2% drop in body water can trigger fuzzy short-term memory, trouble with basic math, and difficulty focusing on the computer screen or a printed page.

"Fact" 8. Drinking 5 glasses of water daily decreases the risk of colon cancer by 45%, plus it can slash the risk of breast cancer by 79%, and one is 50% less likely to develop bladder cancer. Are you drinking the amount of water you should drink every day?

The information in this e-mail appears to have come from the book Your Body''s Many Cries For Water, written by Dr Fereydoon Batmanghelidj, Allen said. According to his biography at www.watercure.com, Dr Batmanghelidj, who passed away in 2004, was an MD.

"From what I can tell, he says he arrived at his conclusions through reading, not research," Allen said.

The watercure.com Web site says Dr Batmanghelidj initially discovered the healing power of water while imprisoned in his native Iran. He wrote Your Body''s Many Cries for Water in 1992. In the book, he states: "The body signals its water shortage by producing pain. Dehydration actually produces pain and many degenerative diseases, including asthma, arthritis, hypertension, angina, adult-onset diabetes, lupus and multiple sclerosis."

While the e-mail has a basis in fact, most of the claims it makes cannot be substantiated. For instance, Allen was unable to find the University of Washington study referenced in point No. 4, and Dr Williams was also not aware of the study. Allen and Dr Williams agree that many people are chronically dehydrated, but the 75% figure mentioned in point No. 1 has no proof.

"I have read 50%, but either way it is a large segment of the population," Dr Williams said.

"[Dr Batmanghelidj] claims his ideas represent a paradigm shift that required him to self-publish his book," Allen said. "So basically he''s saying he thinks people need to think more about water, to which I agree. But I can''t find anything, like a scientific study, that conclusively says 75% of Americans are dehydrated. It may or may not be true. I think it''s a little bit high."

While researching the claims in this e-mail, Allen found a comment by Dr Robert Alpern, dean of the Yale School of Medicine and former dean of the University of Texas Southwestern Medical Center, who said the notion of widespread dehydration has no basis in medical fact.

"Everything I found says, by all evidence, we are a well-hydrated nation," she said. "In general, Americans drink a lot. It may not always be water, but you''re getting fluid from anything you drink. You may be getting other things, like calories or sugar, or minerals, like calcium from milk. But you''re still getting fluid from it. And that''s a good thing."

The widely accepted belief people need to drink 8 cups of water a day isn''t necessarily true for everyone either.

"Nobody knows how that number was arrived at," Allen said. "The key is, you need to look at how much you are losing."

Athletes who perspire a lot or people living in hot climates will need more water, she said.

"A real good indicator is to look at your urine," Allen said. "If it''s real concentrated, you''re not drinking enough. If it''s pale and yellow, like a Post-It note, you''re probably hydrated."

As for point No. 5, about lack of water being the primary cause of daytime fatigue, Allen said, "I wish it were that simple."

In addition to the amount of sleep a person gets, diet could also be a contributing factor.

"If I had a client who was fatigued, I would tell them to look at what they are eating for lunch," she said. "Because they may be getting a spike from eating a meal that is really high in simple carbohydrates. They might need to pair it with some protein that will stay with them a little bit longer. So instead of eating crackers at lunch, I would eat cheese and crackers, or peanut butter and crackers. That would help with your concentration, it would help you to not feel hungry, and it would help keep your blood sugars a little more stabilized so you''re not feeling that fatigue."

The last point in the e-mail, the claim that drinking 5 glasses of water will substantially reduce the incidence of certain types of cancer, is the point experts question above all the others.

"I think drinking water is great, but I am not sure that it would have this impact on malignancy rates," Dr Williams said. "It just sounds too good to be true."

Allen also disputes the figures.

"I don''t know that it''s going to decrease the risk by the astronomical percentages listed here," she said. "But drinking water helps clean out your system, keeps things moving along. ... It probably would help decrease your risk of those [cancers]. But I don''t know that it''s going to decrease your risk of breast cancer by 79%. I found nothing to validate that number."

The bottom line, Allen said, is water is really important for everyone.

"We all need to be drinking water," she said. "But don''t obsess over it—you''re probably getting enough."