Water in the footwell

Generally, you could find out where the water is coming from judging by the traces of water or by removing the footwell carpet and asking someone to pour buckets of water onto the car. If you have a sunroof fitted, this is the first place to check. There are water drain channels in the C pillars, if one or both of them become clogged, water accumulates above the headlining and comes down generally behind the B pillar trim.

Even without a sunroof it might come from the roof. Give it a try by pouring water between the roof and the roof panel side edges. It should come forward to the windshield and run down to the front wings in channels at the side of the windshield, appearing finally on the ground before the front doors. These channels are not closed from the inside, thus, if they become clogged somewhere, the water accumulates there and gets into the car, running down somewhere on the side wall near the glove compartment, getting under the carpet. In my case there was some obstacle at the lower corner of the windshield, easily cured after carefully peeling back the black rubber seal at the corner of the windshield. If it won't come off or you find no evidence of clogging, you can gain access to the problematic areas from the inside, too, by removing the A-pillar trim (sliding upwards). If necessary, you can use silicon sealants (used in kitchen and bathroom; or even better: special sealants because the common silicone one emits acidic fumes that my cause corrosion while curing) but take care to leave the water channels free and seal only where water can go astray.

Another common cause of a wet carpet in the footwell is the leaking heater matrix.