What is causing a water leak in the passenger foot area of my 2004 mustang

Does it have A/C? When I have been running the A/C in my car I noticed a bit of condensation on the passenger side, My truck leaks on the passenger side when it rains. Other wise need to determine if it is coolant. Possible heater core leak.

Thanks joke mom. Wife noticed it last night with a/c on, she thought it was water.

If its water, then the drain hose could be cracked, if its just a clogged hose look under the car on the passengers side for where it exits the car near the firewall and blow some air into it to unclog the hose, good luck..

I had this happen to me and it’s none of the above! The issue is the two compartments between the firewall and the dashboard that allow water to drain away from the hood and windshield. If the holes at the bottom get plugged, water collects until it reaches the height of the air filter, then pours out into the passenger seat. Take off the covers - shouldn’t require special tools - and use long pliers to pull the rubber plugs/valves out of the bottom. Rinse out with a hose and put back in and problem solved!