It has not rained for a few weeks where I'm at yet I've noticed a persistant dampness in the passenger footwell and under the passenger seat.

It seems like it's coming from under not from over. I had a top mat in my passenger floorwell and the top was not wet what so ever but i pull it up and the carpet under is damp.

Not a great judge of scent but smells like wet dog to me so I'm guessing some sort of water clog/leak not oil.

Any ideas what this is?

 

Do you have a sunroof? The same thing happens to mine every so often and the problem is caused by blocked sunroof drains- they drain down a pipe in the A pillar and out just behind the front wheel well, and water may leak out and into the interior if they're blocked