Oh, but Craven you can drink too much water. It can actually kill you.
Noakes, a specialist in human biology at the University of Cape Town, said that much of the conventional understanding about water consumption during exercise is not based on evidence, and that drinking too much is unnecessary and can be fatal.
He cites the example last year, when a woman in the Boston marathon in the United States died from hyponatraemic encephalopathy - a severe lack of salt in the blood - because she ingested excessive volumes of a sports drink before and during the race.
But her death was not an isolated incident. Shortly after a doctrine which encouraged those in training to drink the maximum amount they can tolerate became popular, 250 reports of the hyponatraemic encephalopathy appeared in medical literature, Noakes said. The cases were occurring in athletes, army personnel and hikers, and seven were fatalities.
http://www.abc.net.au/science/news/stories/s904374.htm