If you left the vent open, or if the vent under the windshield is full of leaves, it could cause rainwater to flow into the floorboard.
Passenger's side? Could be a leaking heater core
Water.
A leaky door seal or windshield seal
water in passenger floorboard, where is the hose that would cause this?
your ac might be clogged or your draining hose is clogged. its in that area
I BELIEVE THE WATER COULD BE COMING FROM YOUR AIR CONDITIONING .
the ac condensation drain hose is plugged or crimped.
Water from my ac is draining in side the floorboard where is the drain hose on a 99 Oldsmobile intrigue
It could possibly be the heater core Check your heatting and a/c
A damaged heater core will cause coolant or water to leak onto the passenger floorboard.
Pot hole
normally you have no heat and,or water on the passenger floorboard