2000 Nissan Maxima Leak on floorboard

Check the drain tube from the drip pan under the evaporator for blockage. It is supposed to catch condensation from the evaporator and run it outside. The tube is typically 3" - 4" long, with a right angle bend, hanging on the front passenger side of the firewall. Squeeze it to open it up. If just a trickle comes out, there will be a wire ring you can squeeze to release the tube from the drain pipe. Gently poke a pencil into the pipe to dislodge the leaves / dirt / mouse nest parts.

Caradiodoc

Well, ... It's obviously your own fault. You must be driving in the rain too much, ... Or making too many right-hand turns! :)

Next I would find a friend to wield a garden hose to spray water onto the car while you watch under the dash. In particular, spray around the windshield and wiper arm pivots, but specifically avoid the sun roof area. If you see water running in, you can rule out the sun roof.

If no water appears, then head to the sun roof. Hopefully you will find the drain tube mispositioned or disconnected.

Also look for a missing seal at the rear of the hood that seals the well between the firewall and windshield. Water that gets in there is supposed to drain to the sides. If the drains are blocked with leaves, water can build up high enough to reach rubber grommets where wire harnesses go through. I suspect you would have noticed that before now.

Caradiodoc