Body & HealthFact
The rule '8 glasses of water a day' has no source.
In 2002 a kidney physiologist searched for the scientific evidence behind the 8-glasses rule and found none. One likely root: a 1945 US recommendation that named about 2.5 litres of water daily, but added in the next sentence that most of it is contained in solid food. Coffee, tea, soup and fruit all count toward your water balance.
Useful: In healthy people, the thirst system regulates water balance precisely without counting glasses.
Source: doi.org