Seeing the symptoms, I believe it’s the display module. The phone still works as it vibrates when switching it on, and charging seems to work as well. I’d give this problem a 90% chance to be the display (though something else could have been damaged by the water as well and you can’t see it). So if you don’t have one handy or don’t know anyone owning one, I’d just buy a new display module. If it’s not the problem, you can still sell it on the forum #market.