Technically a brand new iPhone 11 can go underwater but the iPhone 11 is not waterproof. Generally iPhones are built to withstand some water penetration but won’t always survive a drop in deep water or being submerged for an extended period of time. The iPhone 11 is rated IP68, so it's water resistant up to 6.5 feet (2 meters) for 30 minutes.
The iPhone 11 Pro and iPhone 11 Pro Max can go deeper: up to 13 feet (4 meters) for 30 minutes. Although the iPhone 11 does have a level of dust and water resistance, Apple has noted that this resistance is not permanent and may decrease with time. So that means that on a refurbished or second hand phone the resistance might not be as strong.
We like to say that some intense rain might be okay...the toilet, you might not be quite as lucky and we wouldn’t recommend swimming with your iPhone! 🌊🚫. Your iPhone 11 could likely survive being submerged in the water but you should always let your iPhone dry out completely before inserting any cables or trying to turn it back on.