In 2016, Apple has finally sailed. iPhone 7 was announced to have received an IP67 rating "under the IEC standard 60529." In simple words, iPhone 7 was announced to be waterproof - and that's a major plus!
Ingress Protection Rating (IP) is a standard that provides information on the stability of a product against intrusion of stress and other external factors (solid objects, accidental contact, dust, and water in electrical enclosures). IP aims to provide specific information and details on marketing terms like, as in the case of iPhone 7, "waterproof".
iPhone 7 is rated IP67; which means that the device can be immersed in water between 15cm and 1m deep for a certain period of time. IP67 relates to freshwater protection meaning it cannot withstand the ocean. Therefore, it is not generally advisable that iPhone 7 be submerged in water.
A few other unlucky units have been battered and beaten to prove Apple's claim of iPhone 7's resistance to water and dust. It is important to note that iPhone 7 is not absolutely waterproof - no Smartphone is.
For instance, Samsung Galaxy Note 7 is rated IP68. This means that Note 7 units are only resistant to dust and water of 1.5 meters deep and for a span of 30 minutes.
Now going back to the basic questions:
Will iPhone 7 survive a quick dip in water that is 5m deep? Yes.
Will iPhone 7 survive being submerged for 45 minutes in water that is 5m deep? No.
Will iPhone 7 survive a quick deep in an inch of ocean water? No.
The practical point here is you should not intentionally subject your iPhone 7 to stress that you wouldn't want to expose your normal gadget into.
Do note that damages incurred to iPhone 7 due to liquid are not covered under the warranty. Therefore, despite Apple's appeal on the durability and strength of iPhone 7, it is not advised to be exposed in areas with absolute intrusions like the ocean or in the shower.
Specifically, Apple's website reiterates, "Splash, water, and dust resistance are not permanent conditions and resistance might decrease as a result of normal wear. Do not attempt to charge a wet iPhone; refer to the user guide for cleaning and drying instructions."
