WHEN IT RAINS MY PASSENGER SIDE FLOORBOARD FILLS WITH WATER.

You have a leak going through a welded area. The factory uses a seam sealer upon building these cars. So to fix this when the entire car is assembled it quite difficult to do. First you have to locate the nature of your leak. If you can see where it is coming from, great. If not you will need to remove many articles from your car such as the carpet and backing which will have to be removed for proper cleaning from stagnat water sitting in place for sometime now. Any sound board padding going up behind your dash up through the firewall. When all that is removed you can see alot of sheet metal. Inspect all welded seams for traces of rust. That will be an earmark for a leak. Shine a flashlight as far as you can see looking for rust scales throughout.If you have to mix Arm & Hammer baking soda with water 50/50 mix and pour throughout the outside screen into the firewall and watch for that milky film seep into the interior. The soda will ellimanate odors as well for your car. I know this is a tough job which no mechcanic likes to tackle but it does happen to all of us at one point in our lives
Hope you find the leak and get it resealed with a 3M resealing product too
Good luck

It's the cabin air seal, they leak often, pull the cowl and reset the gasket

If it is coolant, it is a leaking heater core. If it is just water, the A/C condenser drain line is plugged. Crawl under the vehicles passenger side and find the drain line. Use a blunt object such as a pencil to unclog it. One other remote possibility is a leak at the windshield