What do iPhone and Apple Watch water resistance ratings really mean?

The iPhone XS has a dust and water resistance rating of IP68. The '6' in that rating means that it's protected from dust entering the chassis, while the '8' means that it's protected against immersion in up to two meters of water for a duration of up to 30 minutes. This means that a drop into shallow water shouldn't hurt your iPhone, though you should act quickly to retrieve your phone from the water and dry it thoroughly before charging it.

You also shouldn't worry too much about spills of liquids like soda, beer, coffee, or tea onto your iPhone XS. It should resist those. If your iPhone does get one of these substances on it, Apple advises you to rinse the affected area of your iPhone in tap water, wipe it off, then dry it.

The Apple Watch Series 4 should fair a lot better in water than the iPhone XS, though it lacks the clarity of an IP rating. Instead, Apple says only this about the water resistance rating of the Apple Watch Series 4:

The watch has a water resistance of up to 50 meters, or around 150 feet. You can easily take the watch swimming with you (it's one of the activities tracked by the Apple Watch, after all), and it will survive dips into shallow water quite easily. The Apple Watch is also sweat resistant, so you can use it during your workout.

Apple warns against using the watch for water-based activities that require submersion below a shallow depth or that involve high velocity water. These activities include scuba diving and water skiing. And while you can shower with your Apple Watch, the company recommends against exposing it to shampoos, soaps, lotions, and other such things as the chemicals in them could negatively impact the water seals and acoustic membranes on your Apple Watch.

The Apple Watch also has a specialized mode that allows you to lock the touchscreen when you're planning on heading into the water with your watch. When you get out of the water, you can turn the digital crown as a tone plays for a few seconds. When the tone stops with a "blip" noise, you can use your watch as you normally would once again. That tone is actually used to sonically expel water from the speaker grills, which are protected from water ingress.

Current-generation iPhones and Apple Watches should be able to survive dips into water, or even extended swimming (in the case of the Apple Watch), but you should submerge them out of habit. If you plan to regularly take your iPhone into the water, for example, you're going to want a dedicated waterproof case.

Just remember that, no matter what the water resistance rating of a consumer product is, it's generally not going to be waterproof. Water will eventually make its way into something with even an excellent IP68 rating. Just be careful and treat your devices with a general level of respect. And don't leave them in the water at all.