The only thing water can do is throw off your electrolyte // sodium balance. Extremely low sodium can cause seizure / coma / death.
You need to drink a SERIOUS amount of water to induce this, well over three times what any person would normally drink in a day, even if you drink a lot of water. Either that or if you combine a poor diet with a major excess of water and diuretics you could pull the same stunt, but either way it is really a non-issue to the average person. The only causes I have heard of people dying from OD on water is from sheer stupidity in a big way (woman who died from drinking gallon after gallon of water to try to win a Wii), or from taking E and drinking way too much water. Don't worry about it.