Help URGENT!! Wet driver's side foot well?

[alpenweiss2]

We haven't had our B5 Passat TDI Estate for long, so are still getting to know the car. When we got it about three months ago I read about the problem with blocked plenum drain grommets on this forum and so cleaned the whole lot out and even cut off the rubber cross shaped fins on the drain hole grommets as a precaution! The carpets were not wet but I wanted to prevent an issue arising! So far, so good.

Anyway, three months of trouble free motoring followed!!

Got home today after the torrential downpours having been out in our T4 Transporter, and went to get something out of the Passat. Noticed straight away that there was a puddle in the drivers foot well?? Checked the passenger side and this was bone dry.

I should add that the car was parked on a steep drive with the front end facing downhill.

I have dried it out and also lifted the carpet and dried underneath with a hairdryer? Can anyone advise where the water is getting in? Anyone had a similar problem? I would like to fix it before the next heavy rain.