30 minuten - 1 uur
I had an iPhone 5S with water damage. It was never submerged, but water seeped through a bag it was in and damaged it enough that it would no longer turn on.
After trying to dry it out with no luck and getting some odd screen responses, I decided to open the phone up to clean/dry everything on the inside. I followed the guide to clean all the contacts with alcohol (several had very obvious water marks on them) and when I powered the phone on it began flashing the apple symbol and never booting.
I figured the next step was replacing the battery so I ordered the new one from iFixit. When it arrived I installed it in about 15 minutes (I'd already removed the old one in the interim), and pushed the power button. I fully expected I'd have to restore the phone or replace other components, but to my surprise the phone turned back on and seemed to work perfectly. All speakers and cameras work, and aside from a few water spots on the screen, everything seems the same as before.
Don't bother with rice or damprid, get the phone open and dry it from the inside. You can remove the iPhone pentalobe screws with a razor blade and a steady hand, it's really not that hard.