Is this the first time after a rain this has happened? Many times when that side is wet it is either because the AC evaporator water tube has come off and the condensation from the AC is leaking inside instead of running outside.
Also, when a heater core is bad, it leaks inside and the passenger floor board gets wet.
You might consider sitting in the car and having someone take the water hose and run it over that side of the car. Start low, like at the bottom corner of the windshield and let it sit there. Give it time. If that doesn't leak then move up higher and wait. Do the same then move it up higher. The person on the inside is watching for water. The only other problem with this is the side panels may have to be removed in case it is running behind them so you can not see the water. Try to feel the carpet to see how high up it is and if it is high, wet just in one area. That will be where it is running down.
You won't know if it is simple until you troubleshoot it to see where it is coming from.
Last there is a technical service bulletin of water leaking in at the head liner but you have to have a sunroof. If you have one and would like this let me know.
Friday, October 31st, 2008 AT 1:24 AM