It is probably you Air Condition Unit!
Ask you self did you have this problem last winter, if not most likely it is the ac unit!
Just had my sons Jeep GC with this problem, had a Broke ac drain hose!
Could be a bad, clogged or broke drain hose, a cracked drain housing unit which can either be glued repaired for a bit of money or replaced for a lot more money!
God forbid it is you evaporator unit leaking your talking about $1300 bucks as they have to remove the Entire dash, in which case it is a perfect time to trade it in!
Passenger's side? Could be a leaking heater core
Antifreeze will be leaking in the floorboard on the passenger side, there will be a smell of antifreeze through the vents.
heater core is leaking.
Probably a leaking heater core.
bad door seals
This would be caused by a leaking heater core, or a leak in the plumbing associated with it.
If that water is engine coolant, the heater core is leaking.
your heater core is leaking i would replace it.
The heater core (a small radiator for your heat) is leaking, I would suggest a new heater core as they are about as cheep to replace as they are to repair.
Either the heater core is leaking or you have a leak at the windshield or the cowl. If the fluid tastes sweet it is coolant and your heater core is leaking.
your ac might be clogged or your draining hose is clogged. its in that area
The condensor drain tube is clogged. Find the drain line and unclogg it.