http://sportsmedicine.about.com/cs/.../a/aa051200.htm

The answer is yes. Basically, you can replace too many of your bodily fluids with plain water. Your electrolyte and salt levels get too low and you can pass out. Over time you can die from it.

I wouldn't drink more than 150oz of water per day unless you're doing a lot of exercising. (4hr+)

It can also happen if you have a rapid change in water intake. If you only drank 16oz for 5 years, then over a week's time drank 150oz every day, you would probably suffer from water intoxication.