water in boot

You most likely have a leaking seal in the deck lid/trunk lid area. These rubber gaskets if they get ripped or torn will leak. A new gasket should help. If you have the sunroof option, depending where the sunroof drain tubes run down the body, you may have one of them which is clogged and leaking.

Check to make sure the third brake light seal is still in tact, that is one known issue... and could be covered under warranty.