A puddle of water has appeared in the nearside front footwell of my 1999 Ford Focus hatchback. The rear nearside footwell is also very wet. The car has not been used in the rain, but it has rained heavily in recent days. The car has been parked facing down a slope. I can't see where the water is getting in - the windows are closed, seats are dry and the boot is dry, it's just that the floor is wet. Where could the leak be?