iPhone 8 and iPhone 8 Plus are “precision‑engineered to resist water and dust,” in Apple’s own words, as is the flagship iPhone X model, but the company has not increased water resistance of the new phones as some were hoping it would.
According to Apple’s iPhone X and iPhone 8 webpages, the new devices have exactly the same dust, splash and water resistance just likelast year’s iPhone 7 models.

In other words, iPhone 8 and iPhone X are still rated IP67 under IEC standard 60529. The Korea Heraldreportedback in January that the new iPhones would feature increased IP68 water resistance like Samsung’s flagship Galaxy smartphones.
As a quick backgrounder, the first digit in these IP ratings determines a device’s dust proofing and the other tells you how water resistant it is. The higher the number, the better protection.

A rating of 7 means that “ingress of water in harmful quantity shall not be possible when the enclosure is immersed in water under defined conditions of pressure and time (up to 1 meter of submersion)” according to the International Electrotechnical Commission (IEC).
The digit 0 is used where no protection is provided.
By comparison,Samsung’s Galaxy S8andNote 8smartphones (along with the new S Pen) have slightly better IP68-rated water and dust resistance allowing them to be submerged up to 1.5 meters for 30 minutes.
An excerpt from Apple’s fine print for the iPhone 8 series:

iPhone 8 and iPhone 8 Plus are splash, water, and dust resistant and were tested under controlled laboratory conditions with a rating of IP67 under IEC standard 60529.
It’s also important to stress that splash, water and dust resistance are not permanent conditions. Furthermore, water and dust resistance might decrease as a result of normal wear.

For more info, see the tech specs foriPhone X,iPhone 8andApple Watch Series 3.
Apple’s internal repair guideinstructs service technicians to pull apart a phone and check its internal indicator, which turns red when exposed to water, for any sings of liquid damage.
Both Wi-Fi and LTE models of Apple Watch Series 3 are water resistant up to 50 meters under ISO standard 22810:2010, just like last year’s Series 2. According to Apple, this lets you use your watch for shallow-water activities like swimming in a pool or ocean.
“Apple Watch Series 3 should not be used for scuba diving, waterskiing, or other activities involving high-velocity water or submersion below shallow depth,” reads the fine print.
The original Apple Watch has a water resistance rating of IPX7 under IEC standard 60529, but you’re advised against submerging it. Stainless steel and leather bands are not water resistant.
Again, this isn’t a big deal but is something you should keep in mind if you plan on buying an iPhone X, iPhone 8 or Apple Watch Series 3 and were hoping for increased water resistance.
Liquid damage is not coveredunder Apple’s standard 1-year warranty so keep that in mind, too.