Water is pooling behind front passenger seat. not sure where the water is coming from.

A leaking heater core will allow water to run out of the case under the dash and pool under the carpet.

You should also check that the front windshield is sealed tight around the frame at times roost could have eaten away the metal under the Rubber seal this was the cause at one of my cars.
John

Have you had front or rear glass changed? Is there rust around windshield or rear glass? Have someone run water hose over upper glass...while someone inside car inspects for water trail. Hope this helps.

the spacer bar holding the passanger seat in place is cracked/rusting? If so you will need to get the section cut out and a new plate fabricated to fit and welded in. Check the door seals are intact as well, the water might be coming in there down to the lowest point.

The best way to find this leak is to use a waterhose, make sure inside is dry them start a slow water spary at the front window and only front glass it is better to have someone inside with a light looking to see a stream coming in, after a while and no leak found start moving up to the top and work your way to rear glass but do this slowly to pinpoint the leak the preson inside must look around also.

Is the water only in footwell behind driver seat? If yes, then have you checked the weather stripping around rear door (assuming that it is 4 doors)? My brother had the same problem, and behold it was the stripping around the door. If you find that is the cause, standard household weather stripping added to door frame will work well.

drill a hole through the floor as a quick fix ,if it gets in let it out ,then check for the leak ,try under the firewall where the AC drain pipe is ,it could be the same pipe for drain water coming in from air intake vents

I have a 1993 ParK Avenue, the original owner said that when she purrchased the vehicle new in 1993, she has always had water getting into the trunk, I found water in the passenger rear floor and I assume it is through the trunk, I had water in the trunk, I drilled holes in the trunk , also in the floor of the passenger area, Yesterday I vaccuum the car and the passenger area was dry, I think a little water may enter the trunk but it will drain before it reaches the interior.

Yes, your heater core is leaking. Dash will likely have to come off. Along with everything that is tied into the dash. Best thing to do is to take it to a repair shop. But before you go off to the shop.. take up the carpet coming from your passenger side front..just pull it back. Far as it will go. Then get the car hot. Run your heater full blast. Also place a white rag at the vent under the passenger seat. It maybe leaking into the ducking and flowing out through there. GOOD LUCK!
Here is a link to how to change the heater core yourself...IF you have the proper tools. As it does require you to evacuate the freon...evacuating into the air is ILLEGAL and there is a very very hefty fine for being caught. $10,000 fine I think

This problem is rare. Try to check if the water really is coming from the outside because its possible that the water is coming from the air conditioning unit's condenser.

To isolate the problem, have someone seat in the passenger seat. Wash your car. Ask the person inside the car if he/she sees or feels any water droplets. If the passenger doesn't see or feel any drops. Its possible that water is coming from the condenser unit of your A/C. You need to have your condenser cleaned if this happens.

This happened to me as well, i thought that my car had some sort of leak from the outside. Turns out that it was only the condenser. I had it cleaned and viola. No more water drops