For what it's worth, I brought 2 iphones back to life this past year (iPhone 5s)
One when my friend got pushed in a pool.
Two when another friend forgot the phone was in his pocket before jumping in a lake.
2 dirty water sources for the most-part. They both never attempted to turn their phone back on (this probably plays the most important factor). Dry them off and put immediately into a bag of rice that completely submerges and surrounds the phone. WAIT at least 24 hours (that's what they say anyway).
Both times the next day, the phones turned on with no issues and still work to this day months later.
I also did the same with a Galaxy Note 3. But after the rice, it was still a little funky. So, I submerged it in 99% isopropyl alcohol to help clean out the sediments from the dirty water. Only for a few minutes or so. Then, I dried it off and put it back in the rice for 24 hours. It turned on the next day with no issues... I was shocked.
This worked with the 5S, as well. Also, found out through personal experience of mine (women really know how to get you back if you make them mad). Short of it, 5S worked flawlessly after over 10 seconds in water and powered on. Still took the safe side and turned it off and dried it out afterwards.