To the OP - regarding the submerged Kindle - regardless of whether you get the warranty or not, it might be an idea to put it for a week into a bag of rice to get out all the residual moisture (if any).
I once managed to salvage my iPod touch that way that had been submerged in ... well, somewhere else, I won't go into details here
... and was not working any more. After a week in a bag of rice, it was working again and has been ever since.
Best regards,
Andy