Too much fluid intake during a marathon may not be good as it may lead to hyponatremia
are some simple definitions of this condition. Read this
for more details. As a runner, I always want to reach the finish
line. So if you are interested in summary of the article (it's a long article),
just go to the end of the article.
USA Track & Field (national governing
body for track and field, long-distance running and race walking in the United
guidelines also recommend (on the similar lines) to be "guided by your
thirst" instead of "stay ahead of your thirst". Another useful
article on this condition.