Hi,
it depends how long the phone has been in the water, here is a post were a FP2 survived a “toilet dip”:
I would suggest to disassemble all parts a put them in a box with rice or even better silica.
It seems to me that the phone has been switched on a bit too early. On a vacation my old Nokia phone got totally wet due heavy rain. After several days of drying in a rice bag it worked again.
Good luck!
EDIT: rice is very dusty, so Silica is definitly the better choice!