While water damage sensors on the outside would be silly to tell one if there were drops of water on the outside. . . NOT SILLY, if they told you whether water had actually gotten into the phone. The screen wouldn't let me power down the phone & I have no idea the extent, if any, of potential water damage. Now I'm just trying to see if the phone is dry enough. Apparently everything is still functional EXCEPT the screen.
BTW, Apple certainly makes enough in mark up on all of these phones to 1) pay their sweatshop workers more & 2) to throw in a free phone, even if it is something as stupid as water damage. . . . I would gladly pay as much as I did for my 6 if they could engineer a water-tight design. They can make money of the replacement phones of other stupid things.. . .