Most people are aware that the drinking of plenty of water is advisable, and anecdotal evidence suggests that more = better (up to a point). However, where did the current guideline of ‘8 cups per day‘ come from?
According to Valtin (i) the origin is probably the 1945 recommendation made by the Food and Nutrition Board of the US National Research Council. This stated :
A suitable allowance of water for adults is 2.5 liters daily in most instances. An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods.
The 2.5 litres was changed to 8 x 8 fluid ounce cups in later recommendations, but is otherwise unchanged.
A couple of things are worth noting about this information (which hasn’t really changed in over 60 years). The first is the line ‘An ordinary standard for diverse persons is 1 milliliter for each calorie of food‘. This seems much more reasonable to me – tying water consumption to caloric intake – than simply drinking 2.5 litres of water. It would seem sensible that an athlete consuming 4,000 kCals per day would require a greater water consumption than one getting through 1,500 (for health reasons – we’re not talking about preparing for bodybuilding competions here).
The second is the part of the guideline which seems to have been overlooked in later versions – ‘Most of this quantity is contained in prepared foods‘. I wonder just how much diets have changed in 60 years.
Further observations – there appears to be a strong emphasis these days on ‘pure‘ water consumption. Whilst I always make sure to drink a glass or two of water when also consuming alcohol, coffee or high-protein foods; the bulk of my non-food water consumption comes from green tea. This doesn’t appear – at least in my case – to make any difference whatsoever.
i Valtin H. “Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8×8”? Am J Physiol Regul Integr Comp Physiol 2002;283:R993-R1004