Is the iPhone Waterproof?
Long story short, NO. The iPhone 7, 7 Plus, 8, 8 Plus, and X are all rated as being IP67 splash, water and dust resistant under IEC standard 60529. With the key words being "water-resistant" and not "water-proof!"
By looking at the chart below you can see the iPhone 7 and newer boast the best Ingress Protection (IP) rating for solid particles (6). Those solid particles being dust, sand, and other small debris. However, the iPhone 7 and newer only offer protection against temporary submersion (7) not permanent submersion (8) in water. Adding up to their overall rating of IP67.
In layman terms this means the iPhone 7 and newer can survive being submerged in just over three feet of water for up to 30 minutes. But, there are also some caveats around “water." Water doesn’t mean salt water, or other liquids, just fresh water under highly controlled “laboratory conditions.”
How do they achieve IP67?
The water (IP 7) resistance rating is achieved by eliminating as many ingress points as possible, one excuse Apple gave for eliminating the 3.5mm headphone jack, and by using rubber gaskets around the remaining ingress points.
However, these rubber gaskets do wear our over time. So water resistant the day you bought your iPhone becomes slightly less water resistant over time.
Good & Bad News
So, the good news, these iPhones are far more water resistant that the previous generations. Meaning you don’t need to be concerned about it getting a little wet if you pull it out to text or take photo in a light rain. And you don’t need to worry about sitting by the pool and having someone accidentally splash it. Even if you accidentally drop it in the toilet, it should survive. But, the bad news is, I would never suggest full submersion your device under any circumstances voluntarily. This IP67 rating should just be an assurance in the case of an accidental drop or splash of water!