The recommendation to drink six to eight glasses of water a day is "thoroughly debunked nonsense," a doctor wrote in the British Medical Journal.
There is no scientific evidence to support the recommendation, wrote Dr. Margaret McCartney, a general practitioner based in Scotland.
Some organizations backed by bottled-water makers -- such as Hydration for Health, created by the makers of Volvic and Evian -- say that it's important to drink 1.5 to 2 liters (about 6 to 8 cups) of water a day, and that being even mildly dehydrated plays a role in disease development, McCartney wrote.
However, no such claims have ever been confirmed in studies, she said, and drinking too much water can actually be dangerous by causing low blood sodium levels (a condition called hyponatraemia) and exposing people to pollutants in the water.
"People still think that we're all going to die or our kidneys will shrivel up if we don't drink eight cups of water a day," McCartney told Postmedia News. "From what I can see, there's never been any evidence in the medical literature about it."
Humans' thirst mechanisms are so sophisticated that if our bodies are in need of water, they'll let us know by making us thirsty.
Dartmouth Medical School physician Dr. Heinz Valtin also told The Huffington Post last month that there aren't any scientific studies supporting the eight-glasses-a-day rule and that, to date, he hasn't seen any additional evidence that would confirm the recommendation.
In addition, drinking enough to produce about 6.3 cups of clear or slightly yellow urine a day means your fluid intake is probably sufficient, the Mayo Clinic said.
http://www.huffingtonpost.com/2011/07/14/drinking-8-glasses-of-wat_n_899276.html
