I don't think that water can actually kill you, its basically a natural thing to drink and water is in everything you eat or drink.. You can drink too much water, but everyone has their own limits. I would think you would know when to stop drinking water when you start to throw up water..
It effects your body on a cellular level... it's really hard to drink enough to kill you... but, don't try it, anyway!! You're likely start vomiting before you do any real damage. Drink eight, 8 oz. glasses of water per day; that's the recommended amount... :)
Water intoxication or water poisoning is rare but possible. Too much water in to short a time thins out necessary electrolytes like salt and sodium and potassium. Since these are of vital importance to the function of the nervous system water intoxication can cause death. It doesnt have to be drunk all at one time. Large amounts of water drunk over the period of of day (esp without eating in order to replace nutrients). There are no set levels as it differs person to person. Ine athlete collapsed and died after chugging 16 oz at one time. Her sodium levels were measured at catastrohicallt low levels. Some folks can tolerate more before collapsing. This is why sport drinks and water intake should be balanced together for athletes. Esp those sweating a lot.