Ken Jennings in his blog The Debunker:
[Heinz] Valtin traces the myth back to a 1945 National Research Council pamphlet advising one milliliter of water for each calorie of food eaten, which would indeed be sixty to eighty ounces for most adults. But everyone seems to have missed the pamphlet’s next sentence: “Most of this quantity is contained in prepared foods”
I drink far more than eight glasses of water a day. I’m glad to learn I don’t have to, but I doubt I’m going to stop.