My 89 spg has a pretty big wet spot in the drivers footwell after sitting outside in a rainstorm last weekend. I need to fix this asap to avoid the nasty rustholes i had on my 88 parts car. The seals in the doors are good and the windshield is new. where does this water usually come from?

everywhere... Step 1 should be to remove the floor rusters (those rubber and foam pads under the carpet) which will allow water that gets in to evaporate rather than just collect and NEVER go away. Leaks from where? Maybe sunroof drains, maybe the windhsield seal isn't as good as it should be, maybe the bolt holes from the knee bolster are leaking a little. I find mine leaks differently depending on the angle that it's parked on, leading me to believe I have several different leaks!

You could pull the carpet away from the edges of the car, and have an assistant with a hose, or better yet, a pressure washer while you observe inside the car. you might be able to find some of the leaks that way! As I always say "Old Saabs just leak"

Yep well this car lives indoors and is only driven on weekends so i didn't notice the leak until now after a few months of ownership. The prev owner put in modern sound deadening so i believe only the carpet is holding the water. I took it to a spray wash 2 weeks ago so maybe thats how it got in. From now on hand wash only!

Luke had the perfect solution in the rally car... just take a drill and punch a few holes in the floor to let it drain.

you may want to take the driver side speaker out of dash and have a look at the heater control valve. white crusty stuff up there might point to a leak source.

Common leak areas

Sunroof drains blocked
Windshield gasket not sealing
Heater control valve
Hole in floor.

Delorean is right, those floor ruster pads are garbage.
The rocker panels by the jack points rust out, also there could be holes in the wheel wells allowing water in.
You'll need to thoroughly inspect everything. Remove the front wheels and look around the wheel wells. Inspect all seams and seam sealer including undercoat condition. Clear all the drains in the body. They clog up.

The wet floor in my tan 86 was caused by a torn shift rod boot in the firewall. The boots have been NLA for a while now, and good used ones are non existant. The later style seem to hold up better but we're only used on the last few years of production.

The plastic box for the climate control can be a source of leaks too. The drain that was added post 86 can clog with leaves and sticks and leak past the seal into the pass floor. I had one that had pulled completely off, dumping all water directly onto the floor. The boot diverts it into the wheel well.

Another place to look is the sunroof drain tubes.