It would appear that the Apple iPhone 6S and the iPhone 6S Plus are both waterproof. Both survived a test submerged in bowls of water for a full hour, without any signs of damage at all.
In a video posted by vlogger Zach Straley the two handsets are submerged in separate bowls of water with their timers on. He removes them at regular intervals to test their functionality. Right up to the sixtieth minute they're still fully functional.
Considering both the Lightning port and headphone jack were left open this would suggest Apple has built the phones ready for the wet.
Apple didn't advertised the handsets as waterproof. Perhaps it intended to do so but wasn't satisfied that it could be sold as ready for water. For that reason this could be a fluke, there may be a chance if you try this at home you won't be getting back a fully functioning handset.
But it's nice to know that if the phone were dropped down a toilet or in a pool it will most likely survive the plunge.
We've contacted Apple for a comment but aren't holding our breath for any official confirmation. Maybe it'll be a big feature in the iPhone 7.