Chances are the water damaged your FPC connectors or the LCD/Backlight circuit.
Do the following as soon as possible:
- Open your phone and remove the logic board (follow this guide)
- Inspect the logic board, especially around the connectors and look for corrosion.
- Inspect both sides of the board. Unfortunately, 80% of the board is covered in shields. That's usually where the damage is occurring.
- Put your board in a container with >90% isopropyl alcohol and let it sit for a while.
- Use a soft brush, like a toothbrush and lightly brush away any corrosion you see.
- Rinse in alcohol and repeat.
- Let it air dry for a day.
- Re-assemble and hope for the best.
A professional repair shop that does water damage repair may be able to recover your phone or the data because they have access to pro-level ultrasonic baths and specialized cleaners as well as the skills to troubleshoot your board.