i had this, somehow my car footwells got flooded - i can only assume when i went through a deep puddle fast
its took ages to syphon out and dry off- mould began to grow and i had to bleach the whole inside - its ok now though still not quite dry - fortunately the bleach did not discolour any of the fabrics etc, so i used a lot
if you can, stand in the footwell behind the seat , nearest the centre, and push against the roof, pressing your foot down as hard as possible ... you may find a puddle forming - i used a wet and dry vac to get it all out and a hell of a lot of liquid was hidden under the carpet and sponge etc