The iPhone 7 and iPhone 7 Plus are rated as being IP67 splash, water and dust resistant under IEC standard 60529.
That means the iPhone 7 can survive being submerged in just over three feet of water for up to 30 minutes.
NOTE: Warranty does not cover liquid damage, so invariably you still need a case. I am planning on getting one for mine as well
though i havent tested it myself, am scared but friends have tried it in swimming pool and in this glass of water, we actually left it for 4 minutes.