Back passanger floor keeps filling up with water

My first guess would be a clogged drain from the air conditioner.

check under drivers side carpet under fuel pedal, there should be a small black hose which is supposed to run through a hole in the floor to the outside. This is a condensation drain tube. If it is not draining it will follow channels in floor to the back drv side floor well.

You most likely have a plugged a/c evaporator drain tube. This tube drains away the water that condenses on the evaporator core [the one under the dash next to the heater core] whenever the a/c is running. If the tube is plugged then the water will fill up the bottom of the plastic heater/air conditioner housing until it overflows and leaks onto the floor. This drain is located on the engine side of the firewall, passenger side, down very low at the bottom curve of the firewall and is usually a very short rubber hose about 2" long. It can be hard to spot as there is often a lot of stuff in the way that makes it hard to see. A quick check is to park the car on a level spot and operate the a/c for sevreral minutes. You should soon see water dripping onto the ground from under the car on the passenger side of the vehicle. If you see it dripping then the hose is ok and you have a different issue, if not then you can pretty much bet that the hose is plugged. I usually use a puff of air to blow out whatever has plugged the hose [bugs, debris, etc] which fixes it until the next time it plugs.

there may be a few things causing this, first make sure there no open holes in floor, then check trunk seal and make sure its not coming from trunk, next would be the back window,take a water hose and spray diffrent areas and check for leaks inside,could be also rubber around the back door or rust holes in wheel wells of rear wheels,

Could be a problem with the seal around the tail light on the passenger side.

The first place I would look is the floor board caps. Make sure one or more of them aren't pushed up, allowing water to enter the cabin. Also, because your defroster is probably on while it's raining, make sure the A/C drain plug isn't clogged. It's a small rubber fiting that sticks out from inside the firewall, behind the engine. Simply pull it out and clean it. When you pull it out, you might be surprised to see water coming out of the hole!

Just a couple things to check. I hope this helps! :)

-Jason

It is more than likely the ac plug that is locate behind your dash on the underside of the passenger floor, if you are not handy most shops when generally repair this for under a hundred dollars

check under the dash on the passenger side of vehicle you should see a tube for the a/c check to make sure that it is still attatched it sounds as if the water is running under the carpet to the rear of the vehicle hope this hopes you.

It is most likely coming from a dried up or improperly installed window seal at the bottom of the windshield (under the wiper trim)

Take the trim off and caulk yourself - or have the entire seal replaced.

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could be weather stripping on passenger door bad. does it had sun roof? if it does it could b that