Originally Posted by miamimike

I had exactly the SAME problem in the Exact same car a few years ago.. What happened was 1) lift up the rear carpet--and remove the rubber drain

plug so the water drains out. Under the battery tray--over the years, leaking battery acid had eaten a hole thru the firewall and allowed water to leak in. I fixed mine with clear marine Goop silicone--cost $2. You can check it out if this is the cause by opening the hood and placing a water hose in this area--make sure the area in the back seat is dry and then hose this area down good for about 5 minutes and if this is the culprit--water will soon start flowing under the seat into the passenger side area. Hope this helps--Mike