here is more on it
A preliminary autopsy states that a woman died of "water intoxication" following a water drinking contest for a Nintendo Wii. News10 in Sacramento reports Station 107.9 The End's "Hold your wee for a Wii" contest had contestants doing exactly what the title says. The winner was the person who didn't release their bladder the longest. + Video
http://www.joystiq.com/2007/01/13/woman-dies-of-water-intoxication-after-radio-contest/
water intox is a serious problem, it is acutally rare out of the physc wards.