The water seems to have got in between the LCD. Not sure if its possible for this ipad but the LCD it self is made up of different layers and would have to be taken apart and replace the sheets that are wet, this was easy to do in the earlier versions of the iPhones. The sheets can also be cleaned but that’s very hard because any dust or smug will be left behind and be visible. I would just say you need a new LCD. To get his done at a shop should cost you around $200 or less. Unless someone else knows how to get this done another way. You can also try Apple and just not give them that story and make up another?