Hi Dimitri,
Although I don't disagree with @hellomacos that there could be a fault on the logic board, it's also entirely possible that the screen itself got water damage and the digitizer isn't functioning. I don't know how to tell which one is at fault, the logic board or the digitizer, but at least the screen is something you could replace yourself. For the purposes of diagnosis you could buy a cheap LCD version of the screen to find out if that fixes the problem; at least you wouldn't be out for the full cost of a whole new OLED screen if it doesn't work; of course, if it does then you'd want to go ahead and get a decent replacement screen.