Can a severely water damaged phone be salvaged?
How would I proceed once I have attempted to dry it out for a few days and power it on? Is it worth trying to diagnose and repair?
iPhone 6s Plus 发布于2015年9月25日,有两个型号A1687、A1634，网络制式有GSM、WCDMA，存储容量有16GB、64GB、128GB可选，机身颜色有银色、金色、深空灰、玫瑰金。维修iPhone 6s Plus和前代产品相似，需要螺丝刀和撬棒等。
Well does it still turn on? Have you opened the phone up and check what's corroded inside?
What type of water got into it (drinking, tap, salt, etc.)?
I'm guessing you don't have tools/equipment to handle water damage.
So in my opinion, if it was really "bad" water damage, I'd just take it to Apple and pay them 329+tax for an out of warranty replacement. Unless you have APple care which will be a lot cheaper.
Also, don't let a 3rd party repair place open it and leave fingerprints or any sign of being opened because Apple will then tell you to buy a whole new phone full price :P