There have been studies on the effects of whiskey as a disinfectant, and it works reasonably well as so many old western stories of a splash of whisky on a bullet wound have attested, even if they probably only fictional.
However, as Steve indicated in his answer, as a water purifier, it isn't going to do much. The ethanol concentrations that you need in order to kill bacteria roughly bottom at what you get in whiskey itself. Drop below 30% or so, and I haven't seen any study that shows any effectiveness as those levels.
So, while you could potentially cut your whiskey with a little creek water, and after an hour or so have something that was slightly less potent and fairly safe to drink, it won't give you much in the way of what we might generally think of as purified water. For that, you'll need to stick to water purification tablets or a good filter.