Did it fall in? I had saved a logic board from an iPhone that fell in a toilet. I unplugged the battery, took the logic board out and soaked it in 99% isopropyl alcohol for a minute or two then took it out and let it dry by a fan. I saved the logic board this way. It was a temporary fix but it still works today (was put in another iphone with a damaged board). Hopefully it was just your screen and the water stood there that way maybe all you'll need is a new screen.
First, the motherboard/logic board contains all the information. Secondly, you can switch the motherboard/logic board if it's dead for a working one. If you're still under warranty and haven't repaired/opened the iPhone just take it to apple and they should replace it. I do also think the touch id/home button is unique to the logic board (not sure). If you do switch out the logic board make sure to log on to icloud.com, sign in and erase all data from the logic board you took out so your stuff won't be saved on it. Hope this helps.