Welcome to Android Central, and sorry for the delay! Was the phone really wet? You could try drying it out by putting it in a ziploc bag full of uncooked rice, which acts as a desiccant. Leave it in there for at least 12 hours.
The other thing to consider is if the area over the ambient light sensor is dirty. If the sensor is blocked, and if you have automatic brightness turned on, then it may think you're in a dark area and will dim the screen accordingly. The sensor is usually near the front-facing camera--just wipe that whole area clean.