Hello XXXXXXXX. You have to start by determining whether the fluid is water or coolant. If it is coolant, you have a heater core issue. If it's water, there are two sources. If it is following using your air conditioning, the drain that allows condensation to leave your evaporator case in the dash board is clogged. If the leak is following rain, then the source of entry must be narrowed down to determine where the water came in from.
The drain for the air conditioner is located on the passenger side lower fire wall of the engine compartment. Follow the floor board to where it starts meeting the fire wall. Look for a small black tube sticking out from the firewall. It may even have a rubber boot on it. Remove the boot if it has one and probe the hole. See if it drains.
Your JA Expert,
Ivan
ASE Technician
ASE Tech w/ 18 years in the field. Self employed for 9 years. Member of AUTOLAB radio show.