Just to supplement the Snopes link that Bicker posted...
Recently there have been interesting articles (in O Magazine and Yoga Journal - that I've seen; probably in other magazines) based on studies that show that much of what has been generally believed about water intake does not hold up in scientific fact.
I posted about this back in July in the 'Does it Work' forum;
here's a link to my post, which includes links to the studies
Interesting reading - particularly that second study which found, for example:
- The liquid found in foods we eat counts towards your water intake.
- Despite popular belief, caffeine-containing beverages such as coffee, tea, soda, etc all count towards water intake.
- "Thirst is too late" is a myth.
As someone who used to shoot for a gallon or more of water a day myself, I have to admit that I'm GLAD for this study. Now, I drink water when I feel like it (usually during the day and when I'm working out, tapering off at night) and I've stopped monitoring my water intake.