So the “eight glasses of water a day” meme turns out to be urban legend and not medical gospel at all, according to David Harris’ Science News Salon Blog.
Harris digs up stuff that we wouldn’t otherwise see for days (the water story came from today’s American Journal of Physiology), so I’m glad to see he’s been Slashdotted today.
My favorite part of his summary (given that vendors in New Orleans were repeating this one when I was there for Jazzfest in April) is about another urban myth of water consumption, that

Thirst is too late. The myth claims that if you are thirsty, you are already dehydrated. However, the body’s thirst response actually kicks in well before dehydration.