NOT PROVEN: Drink eight glasses of water per day

It's the myth that just won't go away. Almost everyone thinks they don't drink enough water, but the idea that we all should drink lots of it – eight glasses per day – is based on no scientific data whatsoever.

No one really knows where the eight-glasses idea comes from. Some blame the bottled water industry but plenty of doctors and health organisations have also promoted it over the decades. The source might be a 1945 recommendation by the US National Research Council (NRC) that adults should consume 1 millilitre of water for each calorie of food, which adds up to about 2.5 litres per day for men and 2 litres for women.

According to Barbara Rolls, a nutrition researcher at Penn State University and author of the 1984 book Thirst, this amount is about right for people ...