If you sell a device as waterproof and then it gets damaged by water, that’s obviously a fault: it wasn’t waterproof like it was meant to be.
https://support.apple.com/en-us/108039
> Because it’s not Apple.
It is.
https://support.apple.com/en-us/108039
> These iPhone models are splash, water, and dust resistant and were tested under controlled laboratory conditions...