If your vehicle is showing water leaking onto the passenger side floorboard, here are the most likely causes and the parts you'll need to fix each one.
Condensation from the air conditioning system normally drains outside the vehicle under the chassis. If the rubber drain tube gets clogged with dust or debris, the water backs up inside the HVAC case and spills onto the passenger floorboard.
Leaves, pine needles, and debris can clog the water drains located under the exterior plastic cowl at the base of the windshield. Rainwater pools up and overflows into the HVAC fresh air intake, soaking the cabin filter and dripping onto the floor.
The heater core is a small radiator behind the dashboard that uses hot engine coolant to warm the cabin. If it corrodes and leaks, engine coolant will drip onto the passenger floorboard, usually accompanied by a sweet smell and a greasy film on the windshield.
Sunroof assemblies are not perfectly waterproof and rely on drain tubes routed down the vehicle's pillars to channel water away. If these tubes clog with dirt, rainwater overflows the sunroof track and runs down the inside of the A-pillar to the floor.
A degraded windshield seal or an improper installation during a recent windshield replacement can allow rainwater to seep past the urethane adhesive. The water travels down the inside of the firewall behind the dash and pools on the floor.