I have had a similar issue with water in the floor plan underneath the passenger seat.
Like the gent above, I have cleaned my 2 drains in the compartment for the roof and thought it fixed the problem...
However the water is back again.
The next step is to dust all obvious place with chalk to see if I can locate it.
However, I did wonder if using the air con could be causing the issue and if there there is a drain to collect the excess water has somehow got blocked?
I would love to hear how you resolve this!!!