Most likely it`s the inner door sealant that has deteriorated and its dropping water onto the sills till it spills into the car.
Either that or the pollen filter inst installed correctly, but I`ll bet its the door seals.
Do a search for leaking door seals or similar and all will become clear.
I did the DIY job on mine before last winter and they still hold up ok, all thats needed is waterproof silicone and a screwdriver or 2.