I used a hose pipe, and sprayed it on the wind screen for a minute or two. Then with a light checked around the battery area. Water had gathered, and not run away as it should. Apparantly there is a drainage point under the battery, this has a tendancy to get blocked with leaves and such. When the water fills to a certain level, it runs into the car via the filter area. From this point, belive or not it can run as far as the rear well. Also there could be an issue with your sunroof (if you have one??) Something to do with a drainage point there too....
Please post your findings....
Regards
Tony Henry, November 2008