Claim No. 1: Drinking Water Helps Excrete Toxins
Drinking lots of water is widely thought to help improve kidney function and boost the clearance of toxins. One way it could do this, Goldfarb says, is by a mechanism called glomerular filtration, a measure of the kidney's ability to filter and remove waste products.
But in one study the researchers looked at, increased water intake by 12 young and healthy people actually decreased their glomerular filtration rate. And in another study, the rate did not change over time during a six-month period in which older men drank more water to try to improve bladder function.
In other research, increased water intake was found to affect the clearance of many substances by the kidneys, including sodium. But the studies don't prove any sort of clinical benefit, Goldfarb says.
"What almost certainly happens is, any toxins the kidney is responsible for excreting simply get diluted when the person is drinking a lot of water," Goldfarb says.
Claim No. 2: Drinking Water Helps Your Organs Work Better
Water is retained in various organs, so the thinking goes, and they work better with more water in them.
But Goldfarb and Negoianu say how much water is retained varies with the speed with which the water is taken in. If it's sipped, it's more likely to stay in the body than when gulped.
Even so, they could find no studies documenting that increased water intake helped the organs.
Claim No. 3: Drinking Water Reduces Food Intake and Helps You Lose Weight
Drinking more water is widely encouraged to help weight loss, the theory being that the more water you drink, the fuller you will feel and the less you will eat. "The [medical] literature on this is quite conflicted," Goldfarb says.
"Drinking before a meal might decrease intake [according to one study], but another study found [it did] not."
Even so, Goldfarb calls this claim one of the most promising for further study.
Claim No. 4: Drinking Water Improves Skin Tone
"From a quantitative sense, this doesn't make sense," Goldfarb says. The water you drink will be distributed throughout the body. "Such a tiny part of it would end up in the skin," he says.
"It turns out one small study showed there might be an increase in blood flow in those who drink [a lot of] water, but no one has ever looked scientifically [to see if it improves skin tone]."