Why is water flooding the rear passenger floorboard of my 1996 Grand Cherokee Laredo?

I, too, just recently discovered this problem. A couple weeks later I discovered the entire passenger side was full of water. Hey, that nicely constructed, one-piece carpeting makes a great sponge it turns out!! Pull down the carpet in the front to look for water. I'm willing to bet you have it there, too. It's either the a/c water discharge hose is backed up or you have a rainwater leak somewhere. You can find plenty of info on the fix for the a/c hose clogging. You'll have to drill a hole through the plug, ect. You can find past recall notices on this very problem with very specific instructions to cure it. (or you can remove the entire dashboard) A water leak will just take time. In my circumstance, I read on this site, pulled the carpeting back some in front, sucked out all the water I could, and then used the a/c to see if it happened. After a week, I'm convinced it's a leak somewhere else as there's been no leak from simply a/c usage. But last week I drove from Indy to Hammond in a horrendous downpour for 3 hours, and later found the water in the back seat and - lo and behold - actually the entire carpet was soaked. This carpeting can hold a lot of water!!! So check it out, and good luck to you. After 227,000 miles on my '97 JGC Laredo, this really is the only real problem I've had, so I guess I shouldn't complain...