That just doesn't hold water, according to doctors at the University of Pennsylvania, CBS News correspondent Nancy Cordes reports.
"If you're thirsty, drink," said Dr. Stanley Goldfarb. "If you're not thirsty, you needn't drink."
The researchers looked at all of the studies out there and found no evidence that drinking lots of water has lots of benefits.
Some common misconceptions, as told by passers-by:
As for upping your intake to improve skin tone or reduce headaches: "There was never a scientific basis for it," Goldfarb said.
And despite what all the diet books say, there's also no proof that filling up with water will make you less hungry.
"Those individuals that enjoy going to the bathroom would benefit from high fluid intake. But others definitely would not," Goldfarb said.
So where did the idea of eight glasses a day come from? Nobody really knows.
The researchers argue that a healthy adult only needs to consume the amount of water they lose every day - about a quart-and-a-half, or four to six glasses.
For some, the findings may be hard to swallow.
"I sort of think the more the better," said one young woman. "I don't think you can drink too much."
Maybe not, but researchers say some of our most cherished beliefs about the power of water could be … all wet.