Audi TT passenger footwell soaked under carpet

Hi all

I have purchased an Audi TT Roadster which is around 16 years old, It has been fine all summer but since sat on the drive in our awful british whether, I have noticed the dials steam up and or have condensation which eventually evaporates.  However on a more though investigation it turns out the passenger side under carpet is soaked !!   Without ripping the entire carpet out any ideas where the water may be coming from?  I am guessing its running down the windscreen and not running off as it should and instead entering the car somehow.  No where else seems to be wet, just the passenger side, the underside foam is soaked.  Any advice would be welcomed