It's your heater core, and it's leaking. You need to fix it. It's located under the dash area by the passenger side. You have to replace the heater core, if you mechanical inclined, you can do it yourself. Get some tips from your parts guy at the auto parts store. Keo If the leak appears to be clean water after a rain, it may just be that the gasket at the bottom edge of the windshield (just above the vent intake plenum), has either fallen off or was taken off and not reinstalled properly - allowing rain-water to run down into the blower housing and drip out onto the carpeting. To rectify, simply remove the three screws securing the plastic cover where the passenger-side windshield-wiper rests, pull the cover off and re-secure the ~18" long rubber gasket to the metal frame-edge above the blower intake. I added a bead of silicon calk to help hold the gasket - because the rubber grippers in the gasket had lost their bite and wouldn't hold. A clean-water passenger side leak can also be caused from a clogged condensation drain on the AC. This has happened to my 98 Intrigue, and was fixed by the car dealer Answer I had this same problem. It turned out to be a plugged weep hole from the air conditioning condenser drain line is plugged. Turns out lots of gunk can get in there. The condenser is behind the glove compartment and drains water through the firewall close to the center of the car low down in the engine compartment. I believe you will be looking for a 90 degree rubber elbow. I had a mechanic suction it out with an air hose (he drained about 1/2 gallon of clean water out). He only charged me $10 since it took about 5 minutes and I knew the solution from reading a post on another forum. He suggested not using a hanger or anything with a sharp edge to clean out the weephole since it could damage the rubber around the area and make it worse later. I would probably try this on my own in the future since I expect it to plug again. It's a bit diffilcut to find unless you have the car up on a lift, but not impossible. More info: http://wiki.answers.com/Q/What_would_cause_standing_water_on_the_passenger_side_of_a_1998_Oldsmobile_Intrigue
Have you checked for a pinhole in the HEATER CORE?How do i check for this sorry to be a pain but really cant afford to go to garage at minute hoping i can sort. It is wet from the passenger door to half way across passenger foot well. and no signs of water coming from anywhere. Now that you have mentioned the passenger door, I would take the door panel off the door and check to see if the water DRAIN HOLES at the bottom of the door is plugged up with dirt or anything else. Water might be being held in that space and slowly merging into the door panel and floor mat. Back to the heater core, disconnect the water hoses from the fire wall and connect them together with a short pipe, this will stop the water from entering the heater and you can still drive the car.
Water pan is not something that I am familiar with, but if you are getting water on the floor on the passenger side then your heater core may be leaking, the drain tube for the ac is blocked ( it sticks out through the firewall on the passenger side and can be cleaned out with a coat hanger or compressed air).
I have a 2000 LeSabre and always was supprised to find water in the drivers side floor after a rain. One day while waiting out a thunderstorm, I looked for the leak. I found water running out at the bottom of the door, behind the door panel. I looked for a drain hole in the door, and could not find one. (The water inside the door has to come out somewhere, I just couldn't find where!!!) I then looked at the weatherstrip along the door post behind the mirror and found the weatherstriping was wrinkled. I straightened up the weatherstrip and have not found any water for about a year. High and dry in my Buick