Water damage doesn't usually show itself immediately. It usually takes 24-48 hours for a phone to suffer water damage.
My xperia SP without waterproofing survived falling into a bucket of water, TWICE!It's still my primary phone!
But I don't trust the newer devices
iron wolve, 14 Jun 2016 X isn't afraid to get wet because no one will buy it lolCosts more than Z5 and nearly Z5 Premium I would never buy this and/or recommend to anyone.
Even front speaker is not affected, it should be more sensitive against water, nice :D.
Most of phones actually can be wet like that, but difference with certificate for waterproofing is that, we can be sure that AFTER that you not gonna have problem with it.
Because problem is not dumping phone in water and expecting to work after that, problem is time after that, when humidity is still there and make mess inside of phone.
Even if IP certificate is not that reliable, its still give information that phone will be not damaged after wetting it.
For example its not problem to wet iPhone 6 or Motorola Moto G(3), problem show up after few hours or days, when you see weird behave like restarting, smudges behind screen or battery problems. Something that dont show so quick after submerging phone in water.