Hey I don't know if you've seen this already but this is from Pebble's site and seems legit. I'd avoid opening it if you can - I know mine gets pretty wet and it would suck to trade off one thing for another.
FE504502, FE504503, OR FE504504
These error code indicate issues which can often be resolved by restarting the watch from recovery mode.
To resolve the issue, please follow these steps:
Your watch may already be in Recovery Mode (pictured on right); if not, please press and hold the back, up, and select buttons at the same time.
Continue holding until your watch screen shows a screen similar to the one pictured here.
Open the Settings menu on your phone
Open Bluetooth under Settings and find any Pebble devices
Tap the icon to the right of the Pebble device(s) and forget them
Reopen your Pebble App and follow the prompts to reconnect your watch to your phone
If you continue to experience the issue, or have trouble executing the steps, please email email@example.com with the following
A summary of the issue, including a note that you’ve tried troubleshooting steps above
The serial number of the watch
A picture of the error on the screen of the watch
A picture of the back of your watch, with the serial number clearly shown
The model and color of your watch
Your phone number and shipping address (including your name, street address, city, region, country and postal code) in case we determine a replacement is appropriate
PS let me know if it works! I noticed you marked this as water damage and tbh if mine did that I'd think the same thing.