Water Damage

You have to read the fine print. It's in the page on the XS technical specifications:

iPhone XS - Technical Specifications - Apple

Phone XS and iPhone XS Max are splash, water, and dust resistant and were tested under controlled laboratory conditions with a rating of IP68 under IEC standard 60529 (maximum depth of 2 meters up to 30 minutes). 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. Liquid damage not covered under warranty.

In the support article:

About splash, water, and dust resistance of iPhone 7 and later - Apple Support

iPhone XS and iPhone XS Max have a rating of IP68 under IEC standard 60529 (maximum depth of 2 meters up to 30 minutes). iPhone XR, iPhone X, iPhone 8, iPhone 8 Plus, iPhone 7, and iPhone 7 Plus have a rating of IP67 under IEC standard 60529 (maximum depth of 1 meter up to 30 minutes). Splash, water, and dust resistance are not permanent conditions and resistance might decrease as a result of normal wear. Liquid damage is not covered under warranty.

And of course the warranty terms:

Apple One (1) Year Limited Warranty

This Warranty does not apply: (d) to damage caused by accident, abuse, misuse, fire, liquid contact, earthquake or other external cause;

Did you buy Applecare +? If you did, then you have two instances of accidental damage and would need to pay a "co-pay":

https://www.apple.com/support/products/iphone.html

Here are the terms and repair/price info (for the US):

https://www.apple.com/legal/sales-support/applecare/applecareplus/docs/applecareplusnaen.html