My Scenic had a wet floor due to rain water running down the engine bulkhead and entering through a cable hole where the grommet had come out.
Another cause could be blocked drain holes in the scuttle below the windscreen. These are located right up against the wings and get full of leaf debris. Remove the gunge and pour water in to check that it is draining out. Sometimes the drain tube gets blocked, it is possible to clear it with curtain wire.
Hope this helps.
AcmeUK, August 2009