By Helen Neill
Newsbeat health reporter
There is no solid evidence that drinking eight glasses of water a day will improve your health, new research has suggested.
Experts in America say there is no evidence water flushes out toxins
It is often said that drinking plenty of water improves skin tone, helps dieters lose weight or prevents headaches.
However, experts in America say that there is no evidence to back up the claim that water flushes out toxins.
Doctors Dan Negoianu and Stanley Goldfarb from the University of Pennsylvania, reviewed lots of studies on the issue.
The findings have been published in the Journal of the American Society of Nephrology.
They found that people in hot climates and athletes do need extra fluids, but that there was no data to support the recommendation for normal, healthy adults.
There was no evidence that drinking eight glasses a day helps keep you looking younger, or that it helps dieters feel "full".
British Nutrition Foundation advises that six to eight glasses of any fluid, including tea and coffee, should be enough to prevent an adult from becoming dehydrated.
Claire Williamson, a nutritionist for the BNF, said: "We need water for our bodies to work properly, but that can come from other drinks as well."
She said that she didn't know where the eight-a-day advice had originally come from.
"You often read in health magazines about how important water intake is for your skin, hair and nails, but actually there isn't a lot of evidence there," she added.
However, none of the research suggested that drinking eight glasses a day does any harm either.
The doctors have recommended that there should be a definitive study to find out once and for all whether there is any benefit.