Water in the Boot.

[Zormecteon]

Others may have had this problem. I found a couple of gallons of water around the spare tire, down in that well.
Where is it getting in, and how do I stop it?

 

[Cdnmr2v6]

Mine was coming in through the left (US driver's side) tail light. I tried siliconing the shit out of both sides of the sheetmetal, but it would still seep in slowly, so my fix came in the form of a can of (clear) Flex-Seal. I just went in from inside the car and sprayed the absolute shit out of the area behind the tail light and that did the job.

There are other potential areas to check, sunroof drains, antenna, rear vents under the bumper, etc. You will have to do some sleuthing to try and track it down.