I have a 2001 Buick Century. I purchased it new in 01, Have had very little problems with it. Last night it rained and the passenger floor got soaked. Drivers side was dry. Any ideas where I shold look to stop this from continuing. And yes the window was rolled up :).
Check the drain for the AC evaporator. This drain tube is on the firewall, low on the passenger side. You’ll probably have to raise the car to see/reach it.
If the tube is clogged water condensing on the evaporator, or rain entering the cowl vent, will drip into the car instead of onto the road.
Chances are good mcparadise is correct, rain can cause additional condensation and if the drain is blocked you get a wet passenger side wet floor.
But since it may have involved the rain and if you have a sun roof, it may have a blocked drain or it is more remote possibility there is a rust hole in the floor.
Another possiblity is the sealing at the base of the windshield.