Hi gill,
Here are some suggestions:
1. Does the phone work on headphones/earphones?
2. Is the flight mode switched on?
3. Have you tried the app SoundAbout?
However, since your phone experienced a water damage, there could still be water on the motherboard that causes this issue. I recommend taking the phone apart (using [guide|12696|this guide]). Now lay the motherboard into isopropyl alcohol (90%) for about 10 minutes, take it out of this "bath" and let it dry for a couple of days next to a warm source (air conditioning, for example). Put everything together again and then test it again.
Steffen