Water, Water Everywhere

"...about 55 to 60 percent of the human body is composed of water. Lean muscle tissue is nearly three-quarters water, and even solid-seeming bone contains more than 20 percent liquid. The stuff is essential for movement...Without water stores, the body can't produce the energy needed to propel it to a drinking fountain...

"'Plenty of people still believe that eight-glasses-a-day nonsense,' Dr. Noakes says, although a comprehensive 2005 report from the Institute of Medicine, based on years of study and scientific review, concluded that there was no credible evidence for the widespread belief that we need to drink eight glasses of water a day, especially since a large portion of a person's daily fluid needs can be met through food. Meat and vegetables contain water. So does milk. Even coffee counts toward your hydration intake, since, although it is a diuretic (meaning it promotes urination), you retain more of a latte's fluids than you lose. Drinking an additional eight full cups of water and other fluids 'is likely to be more than most people need,' Dr. Coyle says, 'even if they are quite active.'"

The First 20 Minutes: Surprising Science Reveals How We Can Exercise Better, Train Smarter, Live Longer by Gretchen Reynolds

I had heard that the "8 glasses a day" was de-bunked but now I've got the data to back it up.

Note:

Dr. Timothy Noakes, Ph.D. is a professor of exercise and sports science at the University of Cape Town in South Africa and a seminal if divisive figure in hydration science

Dr. Edward Coyle  Ph.D., is an exercise physiologist at the University of Texas at Austin who's studied the topic for decades and served for many years as a consultant to cyclist Lance Armstrong