2001 Buick Century Water on Passenger Floor

This just really stinks: water on the front passenger floor.  This post is about what caused it and how I fixed it twice on my 2001 Buick Century with a moon roof.   You might think that moon roofs like this seal the water out; well, think again.  The seal keeps a lot of the water out, but not all. The pesky water that gets through is channeled down one of the four drains in the corners inside the moon roof frame.  You see in this first picture what a clogged drain can lead to: a little ducky pool on your carpet and a spongy, wet headliner.  It all dried out ok, but it's happened twice: once a perfectly sized rock was sitting over a drain and only backing up and leaking when it rained hard.  That was my first experience with this sort of problem and was a bit vexing with the garden hose not producing a leak but going out some mornings to find the pool was back.  This second time, there was a beaver dam going, made from old leaves and gunk; same front right drain hole. So if you see this, take heart, it is fixable and can be dried out and cleaned up just fine.

Water drains away though openings in the corners that are connected to drain hoses.

If one of the drain plugs gets an obstruction, or heaven forbid, the drain hose rots or comes off, the water just runs on the headliner, down a pillar or some other unhappy path, and ends up in a puddle. The beaver dam was cleared with the black wire shown.  You can help find a blockage by pouring a little water along the moon roof and watching for a puddle.  That diagnostic can get everything all wet or it can help; just don't go nuts with the water.
I dabbed around on the headliner (carefully, because headliners can get loose and that's no fun), and cleaned the moon roof drain areas thoroughly with household cleaner and a soft brush.

This is where the water is supposed to go down from the right front drain hole.  The drain hose goes down through the pillar, pointed out by my lovely no.2 pencil assistant.

The end of the drain hose terminates in the door just above the lower door hinge.  I'm thinking that's a heck of a place to dump a bunch of water.  Helps keep the hinges de-lubed and rusty.  ~Chuck