I had this on my Meriva, I assumed it was the double sunroof but it turned out to be some blocked draining under where the windscreen wipers were. On mine however the carpet got soaked on the drivers side, passenger side was unaffected.
If I remember there's a video on YouTube, I'll have to check. My mate sorted it for me, but the YT vid shows how to remove the housing etc where you windscreen wipers are placed.