The floor behind the passenger seat gets wet .

What is your question?

The carpet on the floor behind the passenger seat gets wet only on the bottom of the well, Th floor mat is only wet on the bottom. There is some kind of vent there could the water be coming from that?

What makes this problem better or worse?

When the car runs

How long has your 2010 Mercedes-Benz E350 had this problem?

A couple of months that I know of.