First of all, I don't think I have ever seen a better way to ruin your xperia design, bravo.
Secondly, it is basically a sticker and therefor it should hold on the phone without any problems. (unless it's made out of paper (it is not, don't worry))
Thirdly seller lists item as durable and washable so there should be no problems connected to water contact..
That's about it, have a nice day
iPhone 3G 16gb --> iPhone 4 32gb --> HTC Sensation --> HTC One V --> Nexus 4 --> HTC One -> Sony Xperia Z1