COMMON advice to drink six to eight glasses of water a day is based on an "urban myth", according to a review of evidence.
There is also little support for the claim that most people do not drink enough water, according to Margaret McCartney, a GP whose review of published evidence led her to conclude that the advice "isn't borne out by any evidence whatsoever".
A series of previous reviews has failed to find hard evidence for the much-quoted claim that people should drink about two litres of water a day, but the advice continues to flourish.
Dr McCartney writes in the British Medical Journal: "The 'we don't drink enough water' myth has endless advocates. Schools often insist that pupils bring a water bottle to school and tell pupils that they should drink eight glasses a day.
"It says on the NHS Choices website, 'Try to drink about six to eight glasses of water (or other fluids) a day to prevent dehydration'. This is not only nonsense, but is thoroughly debunked nonsense."
She added: "Water is a very good drink and people should drink it instead of sugary drinks. You don't have to be dripping it into you 24 hours a day. We should just relax a bit."
The idea that most people do not drink enough water has been perpetuated by initiatives such as Hydration For Health, which was created by the French food company Danone, producer of the bottled waters Volvic, Evian and Badoit.
A spokesman for Hydration For Health said its advice was "relevant".
The UK's Department of Health said NHS advice was based on a calculation that 1.2 litres of water was lost by the body each day and not replaced by water in food.