Phones have been doing this for years. I regularly take my iPhone into the pool and into the ocean. I get that message for a few hours afterwards. Sometimes if I need to charge I will try to dry it out with a hairdryer.
Do people take their phones into bodies of water? I still worry about mine getting wet when I bring it into the bathroom.
(If Apple, with all their data, think it's a net-profitable offer, I must be net-losing on the deal versus the default of self-insurance. Especially since I am a more-prudent-than-average device owner!)
I wouldn't take it into saltwater though. That doesn't seem great for any exposed contacts... or anything, really, except fish and things that eat fish.