The National Academy of Sciences in the United States did a very extensive study several years ago assessing water intake,” says Professor Goldfarb. I can hear the smile in his voice. “Their executive summary was: drink when you’re thirsty.
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Emine Saner, “Have we had our fill of water?”, The Guardian, 23 July 2011, p. 42-43
http://www.guardian.co.uk/society/2011/jul/22/had-our-fill-of-water