The trend nowadays is to drink water like there's going to be a drought tomorrow. However, water drinking was taken to extreme in the U.S. when a woman died from drinking too much water while competing in a competition to win a Nintendo Wii:
BBC News: Why is too much water dangerous?
This is an unfortunate accident where someone who dropped out of science class as soon as possible to study media studies didn't know that cells swell when given water. If given too much water, these cells will eventually burst.
So there you have it. Too much water is bad for you. Limit your intake to about 2 litres per day (including tea, fruit juice, etc.), and you should be fine.
Next they will be telling you breathing is dangerous!