either a ruptured heater core or a bad hose/ connection on either end, either way u have to take it out.
Heater. Core
Water on the passenger side floor would be a plugged up AC drain. The drain is located under the hood, at the lowest point on the HVAC box on the firewall. However if the floor is wet with engine coolant, the heater core is leaking.
Are you running the air conditioner? If the drain line is plugged, it will leak water (condensation) onto the passenger side floor.
water in passenger floorboard, where is the hose that would cause this?
"I have a 2003 Ford Explorer, the original owner. When it rains, the passenger side carpeting gets soaked. What causes this? I do have a moon roof."
what causes water hammer in pipe systems?
heater core may be leaking or hole in floor
If it is coolant, a leaky heater core. If it is water, a clogged ac drain or damaged door gasket.
Is it blood, oil, water, or urine?
There is a drain on the outside firewall that is clogged.
you could have a heater core leaking or your windshield is leaking and the water is running down behind the dash and onto the floor.
bad heating core