What is the best way to remove a small water stain from a non-waxed wood floor?
Sometimes the best way is to sand the spot out by hand using 80 grit sandpaper, followed by 100 grit. Determine what your floor finish is (by reading the second half of my floor maintenance article). Use the search box at the top of the web page and touch it up with 2-3 coats of this finish. If it is one of the reactive finishes (polyurethane is one of these) it will not blend in well so on the last coat so you may have to re-coat the whole board involved or group of boards. But that depends on how fussy you are.
If you find after the sanding the water stain doesn’t come out, try a spot treatment with oxalic acid. It’s usually the main ingredient in some deck whiteners. Wash after with lots of water after, then fine sand. Let the spot dry overnight and then touch up the floor finish.