From where and why is there water build-up on the passenger side floor board?

not coolant either?

Not that I can tell, or smell. I'll soak some up in a rag and wring it out in a clear container and get back to you.

I soaked up some from the back floorboard and it was brownish color. The coolant at the top of my coolant system is green. Still no "coolant smell."

Sounds like two separate problems, one is a cooling system issue, and the other is an AC drain that is clogged. On the cooling system issue, you can go to Youtube and lookup "Eric the Car Guy" video on how to diagnose a cooling system. From what you describe, after changing the thermostat check that it's a good one and that the springs are installed FACING the engine. Otherwise the jiggle valve won't properly let coolant on the needle of the thermostat and let it get hot enough to open. There MUST be a trickle running through the system while the engine is cold. Another possible issue is your cooling fans aren't working, but since it overheated so quickly I'm guessing the thermostat is still an issue. AS A TEST ONLY, remove the thermostat, re-attach the housing and hose of course, and see if the car still overheats 10 minutes down the road. DO NOT DRIVE PERMANENTLY WITHOUT A THERMOSTAT.

Thanks, Joshua. I'll give it a try. I have yet to figure this one out. The guys at work say my heating core is leaking and my fan (not an electric one) is not running hard enough (air flow) to cool as well.

It's possible the clutch is worn out in the fan causing the overheating issue.

How did you soak it up? with a shop vac? or some paper towels...a hair dryer? is it dry or still spongin' it on up?