Expatriate international health insurance customers may be some of the people who believe that it is essential for good health to drink at least eight glasses of water a day.
However, GP Margaret McCartney commented during a podcast with Duncan Jarvis of the British Medical Journal that this "has been thoroughly debunked at least twice" by the peer review process.
"There has never been any evidence" that people should consume more water than they would like but "it just seems to be perpetually repeated", she continued.
She noted that a BBC report several years ago claimed that drinking water makes children more intelligent and better at concentrating, but this was not a scientific study.
Some websites still cite this report as a "good reason to tell children to drink more water than they would normally", she added.
The NHS responded that the debunked studies Ms McCartney refers to recommend drinking 1.9 litres daily, rather than the 1.2 it advises.
It asserted that the purpose of this is merely to keep hydrated and replace water loss, "rather than to obtain any broader health benefits".