You dropped you phone in water, but don't think it has water damage?
Drop any electronic device in water, dry it out and wait a couple of months.
Open it up and notice all the green corrosion around terminals. That's water damage.
I used to work in a store as a technician, and I would see a phone similar to yours once a day at least. Same explanation: I dryed it out and it worked fine. Once you open it, it becomes a different story. Symptoms are usually the same also. Phone powering off by itself, screen blanking out, and just odd problems you don't normally see with a phone.
If you didn't open the phone and dry it out immediately, the water evaporated inside the phone. Even if you did, it's a crapshoot after you dry it out and close the phone back up.