The well known site, SquareTrade, made a breakability test for both new iPhones; they tested their sliding, water resistance and drop test.
The iPhone 6 survived more than the 6 Plus in their drop test; after 6 drops, no screen cracking and it’s still good for using.
When the phones got into water, they were playing music. 10 seconds later, music stopped. After getting them out, they’re working and no damage happened, and as said: few minutes later, the sound worked again.
After all that, Apple didn’t call its phone a “waterproof” one. May be they’re not sure enough about their phones ability to survive in water without any fuss.