Hi there. I have exactly same problem on mine C5 (2009) Tourer. I found out where water is coming in, but I cant find from where... Open the plastic cover on front column ( between doors and dashboard). You will see a white plastic "pin" with black rubber gasket which holds the plastic interior decoration. Remove it (dont brake it!) and watter wil run out just like water-tab opened! (prepare a bottle first ;)) The column is filled with water and also your lower part of carpet which is difficult to dry. I sucked all the water from the column with a small rubber tube, but it's getting in on every rain. If you find the reason/place where rain can enter the collumn please let me know! Service personell of Citroen is uselles here in Slovenia... Regards, Gregor