iPhone XS Max Waterproof?
Do not put the iphone underwater!
The iPhone XS Max is not waterproof but it is water resistant up to a depth of 2 meters for up to 30 minutes. Apple's iPhone XS Max is certified as waterproof rating of IP68.
Devices backed by an international standard rating of IP68 are deemed fit enough to withstand dust, dirt and sand, and are resistant to submersion up to a maximum depth of 1.5m underwater for up to thirty minutes.
Play it Safe!
This doesn't mean you could bring the iPhone into the pool to take underwater pictures without an underwater case. (Don't forget the damage salt water or chlorinated water could do to the case.)
Highly Advised to Use a Case!
What this means is that the phone should function fine in a normal rain storm. If it should get place in water, it may stop working. Worst is that if it does stop working, the water damaged phone isn't covered by Apple's Limited Warrantee. Trust me - Apple will know that the damage was caused by water.
If you plan to take any underwater photography, protect your investment and use an underwater case!