Wet floorboard behind passenger seat in 2005 Honda Accord

The carpet behind the passenger seat is soaked after driving 2 hours today in the rain. No water in trunk or spare tire well. Windows and doors closed. Where is this water coming from?

Sunroof? If so, check the water drains in the corners are clear.

If you suspect them, use a long piece of heavy gauge weed-whacker string to clean them.

Just an after thought, do you park under trees? The plugged drains may be due to that.

Check the fresh air vent drains below the windshield as well.

Exactly what Roadrunner wrote. It is very common with sunroofs. If you don’t have a sun roof let us know.

There is no sunroof. It is parked under trees.

Your AC drain is possibly clogged causing the water to spill over into the cabin and settle to rear(possible low spot). I imagine you ran the defrost(A/C) during this time?

With out a sunroof, my next suggestion would be the door. There may be a blocked drain or just a bad leak letting water in.

The fresh air vents are clogged with pine needles. How does that lead to water in the back floorboard?

Lets try another tact.

Is this vehicle a 4 door?

If so, what condition is the weather-stripping in ALL around the door.

Does the rubber seal against the window (On the outside of the glass) really seal the water out, or will it allow water to bypass it and perhaps fill up the bottom of the door.

Perhaps enough to have water drain through an opening in the inside of the door and onto the floor?

If the drain holes in the bottom of the doors are NOT clear, this MAY be what is happening.

Then again, perhaps its something else, maybe a hole in the floor pan?