"If you want to throw away your water bottle, feel free to do so," said Stanley Goldfarb, a researcher at the University of Pennsylvania.

Goldfarb sifted through mounds of medical research and concluded, when it comes to water making you healthier, "it really is something that's come up through folklore rather than through science."

Goldfarb looked for evidence that water flushes toxins out of your system:

"There really isn’t any; there’s virtually no evidence for that," he said.

What about improving skin tone or relieving headaches? There’s no evidence, he says.

Goldfarb did find there's some benefit to helping you lose weight. Fill up on water before meals and you eat less. But there's no evidence that weight loss will last.

The idea of eight glasses a day came from a Food and Nutrition Board recommendation, but that included water in all the food and beverages we consume.

Even the bottled water industry won't say water is healthy.

"We don't make health claims for bottled water. What we do say is water, whether it's bottled water or whether it's tap water, is essential for life," said Joe Doss, a spokesman for the International Bottled Water Association.

The Institute of Medicine says most healthy adults do fine without excess water -- just drink when you're thirsty.