Usually this is caused by a leak in the seal around the windshield. The water then runs down the body behind the trim where you can't see it and pools on the floor. I had the same problem. I found that there is a foam strip on the cowl that was squashed. The foam being squashed allowed the water to run down the windshield under the cowl and into the blower housing, the housing then leaked onto the floor pan in 2 locations (corner and middle) by the firewall. A new foam strip will help, I also used a piece of body moulding on the metal lip above the air filter to divert any water. So far so good!
If it's the front passenger side ,I would say your heater core is leaking .
Windshield seal? Lower door seal? Hole in floor ?
It could be the heater core leaking.
Heater core has failed.
clogged or damaged catalytic converter
Heater core
most likely cause is your heater core leaking
Leak in heater core
The ac drain is plugged. The drain hose is on the firewall on the lower passenger side. ...that, or your heater core is leaking.
It fastens to a pass through stud at the passenger floor.
it is on the floor, passenger side under the heater unit The inertial fuel pump switch is located on the passenger side floor board, just at the edge of the carpet at the firewall, and just at the left edge of the transmission tunnel. It is black, about 3 inches by 3 inches with two wires exiting the bottom. No parts need to be removed to see it.
If you have been running your air conditioner, it's possible that your drain hose is clogged, and the condensation is dripping in. It is also possible that you have a leak in the heater core or a windshield leak.