Here is some advice from Land Rover Forums.com, where more tips and fixes are available.
Air con drain
There seems to be a wet patch on the far left hand passenger side floor. I don’t think it’s coming from the door or leaking from anywhere above as the ceiling is all dry etc. I did some research and discovered that it could be a sunroof or air conditioning drain could be clogged?
I would check the air conditioner drain first. There should be two, and they come out near the transmission. Look for two pointed rubber ends that can be removed, cleaned and reinstalled into the rubber pipes. When I did mine about a half a gallon of water soaked my shirt sleeve.