I recently noticed my Mazda 3 has water leaking in the trunk on each side by the taillights and also on the driver side floorboards in front and back seat. Has anyone else had this problem or know a way to fix it? Water is getting in whenever it rains.

 

Not sure if it's the same problem or not, but here goes. My friend called me one day saying she had spilled a bottle of water in her Mz3i sedan and needed help pulling up the carpet to dry it out. After a little tinkering I deduced that she either spilled a 5 gallon jug of water or that there was another source as the entire passenger floor was soaked from the firewall to the gas tank.

Turns out the drains in the bottom of the rear passenger door were plugged up with gunk. Since water infiltrates the outer layer of the door through the window channel those drains are necessary. With them plugged the water collected until it overflowed into the interior through the speaker hole in the door panel. Then it soaked everything in it's path.

I was able to pop the drains out of the holes in the door, rinse them out with clean water and reinstall them after the door finished draining. For drying the interior I had to remove the front and rear seats, the center console, and the PJB. Then it was just about 45 minutes of open air drying and focused hair dryer use to get it dry.

Sadly I wasn't able to dry out my car as well when I accidentally left all the windows and the moonroof open during a torrential rain storm. It rained for 2 days straight, and then I was working 12 hour days the next four days. I ended up with a fantastic mildew result, though that's waned over the years. One of these days I'll rip out the interior and see if anything can be done to mitigate it short of replacing the carpet and padding.