The SEAT answer is crap.....yes of course rainwater is allowed to flow down the outside of the glass, through the door and drains out at the bottom to the outside...as long as there is a moving sheet of glass, there is no way of waterproofing the inside of the door completely against rainwater, so it is designed to get wet inside and allow the water to drain away through the drainholes.
That is why there is a moisture barrier inside the door card...too keep that rainwater away from the inside of the car, and direct it away through the designed drain channels.
However there is no reason on earth that water should find its way to the inside of the cabin, especially gathering on the inside of the glass.....any moisture inside the car will cause fogging up in cold weather when the heater is on. (Ever get into the car with wet clothes/ hair after a shower of rain ??)
I want to locate the cause of this myself, its happening on only 1 window at the moment, the passenger front window. It's obviously a window seal issue somewhere. Luckily my local
Dealers are fairly approachable and honest about stuff, so if I cant fix the
problem myself, I will let them have a go...
BTW, This is the fourth SEAT that I have owned, all different models, and the fourth that has leaks inside the cabin. No SEAT is ever 100% dry at all times....bit like a FIAT !!
E.g.: Arosas and older Ibizas fill up inside due to rear wash/wipe plumbing connections disintegrating behind trim and thus filling up the car with screenwash, my old MkII Toledo nearly broke my heart with wet footwells where all 4 doorseals leaked rainwater from inside the doors into the footwells, and had a leaking pollen filter cover, and had a leaking plenum chamber panel (in front of driver's seat). It was like a scene from Das Boot....as soon as one leak was fixed, water poured in from somewhere else !
If you dont have wet glass, but your windows fog up badly (with clean glass !) then check the carpet in all 4 footwells....press down well with your knuckles as the padding underneath is very thick and absorbent. Check the boot carpet also.
I believe that new Alteas and Toledos have a common fault with wet passenger footwells where the drain pipe from the aircon unit to the bottom of the car splits and leaks water into the footwell. The ironic thing about this is that if you have the wet window
problem and you use the aircon to dry the insid eof the car, if you also have the aircon drain hose
problem, the condensed water from the aircon condesnser pours into the footwell instead !!