Hi, Mike.
I'm pretty sure I know the problem you're having. The water is leaking... somehow... through your passenger door and ending up on the footwell floor?
I was able to diagnose this problem by placing blue paper towels (shop towels) in my door sill and flooding the car with my hose-pipe. I put a camera in the car and video-taped it while I hosed it down. When I concentrated the water spray at the intersection of door and window, I saw the water soak the towel inside the car.
The problem is with the vapor-barrier inside the door. It is sandwiched between the interior trim card and the metal, exterior structure. The thing is designed to catch water coming in and allow it to drain out of the doors, but it can become un-sealed. This is a known E90 problem. Google around for "E90 door vapor barrier" and you, too, will become an expert on this issue.
I used this excellent DIY video to take my door apart, re-seal my vapor barrier with new Butyl Tape, and re-assemble. Good luck! I got the tape at Home Depot and borrowed the tools from my dad. You'll need a T20 driver set and plastic trim removal tools. If you don't already have them, they're useful to have around.
We also needed a lot of elbow grease and some pliers, as removing my door panel was harder than in this video. The panel was "stuck" on with some sort of rod directly behind the curved trim piece you use to pull the door shut. We had to fuss with it (after having already gotten out all the fasteners) and pull until it came off. One suggestion: head to the dealership and acquire some extra fasteners for the door panels. There are little white plugs and grey "christmas-tree" shaped plugs. You will likely break some of them and it's nice to have them on hand. If you don't use them all, return them later.
Incidentally, it's good to know how to take apart the door panels incase you ever have a door lock actuator or window regulator fail.
Best,
Alex