Is Xs waterproof

No, it is not waterproof. Here is the fine print: iPhone 7, iPhone 7 Plus, iPhone 8, iPhone 8 Plus, iPhone X, iPhone XS, iPhone XS Max, iPhone XR, iPhone SE (2nd generation), iPhone 11 Pro, iPhone 11 Pro Max, iPhone 11, iPhone 12 Pro, iPhone 12 Pro Max, iPhone 12, and iPhone 12 mini are splash, water, and dust resistant and were tested under controlled laboratory conditions; iPhone 12 Pro, iPhone 12 Pro Max, iPhone 12, and iPhone 12 mini have a rating of IP68 under IEC standard 60529 (maximum depth of 6 meters up to 30 minutes); iPhone 11 Pro and iPhone 11 Pro Max have a rating of IP68 under IEC standard 60529 (maximum depth of 4 meters up to 30 minutes); iPhone XS, iPhone XS Max, and iPhone 11 have a rating of IP68 under IEC standard 60529 (maximum depth of 2 meters up to 30 minutes); and iPhone 7, iPhone 7 Plus, iPhone 8, iPhone 8 Plus, iPhone X, iPhone XR, and iPhone SE (2nd generation) 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. Do not attempt to charge a wet iPhone; refer to the user guide for cleaning and drying instructions. Liquid damage not covered under warranty.

Important to remember that the IEC standard is a test under ideal conditions with brand-new iPhones, not a guarantee of some sort. As Lawrence mentioned, water damage is specifically excluded from the warranty. And the phone has a detector inside that will tell any repair person that water got in.

For example, just because the IP68 rating means that an iPhone 12 may "resist" water down to 6 meters for up to 30 minutes does not mean that it is safe to immerse it in any depth for any amount of time or to expose it to flowing water.

Hopefully your XS will behave normally once completely dry, but it does not you will need to pay for a repair (if even possible) or buy a new phone.