Drinking too much water can actually be fatal. Usually from a build up of intercranial pressure as your brain swells. This is, in part, on account of hyponatremia, which is too little salt (specifically sodium) in the blood. Which is bad as the sodium is an important electrolyte for normal cellular functions to take place and helps balance the proportion of water in and outside cells. When the balance is reverse, water can flood the cells causing them to swell and potentially burst. If these are brain cells, that's bad.
But we are talking 10-20 litres in a couple of hours or something silly. Death is unlikely, as that is A LOT of water, but making yourself seriously unwell is a distinct possibility if you chug 5 or 6 litres an hour, which is far more feasible to actually be able to consume.