Apple's new iPhone 7 and iPhone 7 Plus are the first dust and water resistant iPhones with IP67 protection, meaning they're 100 percent resistant to dust and sand and should survive being submerged in about a meter of water for up to 30 minutes. The devices have waterproofed components like the buttons, the chassis and the SIM tray.
Plus, they most likely use gaskets and seals like other water resistant phones. But if water does make its way into the device and damages it, don't count on Apple to replace it at no charge because liquid damage is not covered under its warranty.