Removing water stains on wood floors; sanded and still have water stains!

Q: I have a question about removing water stains on wood floors. I have sanded a floor. Now I have to remove some water stains that are still visible. How do I do this without more sanding?

A: Some water stains won’t sand out regardless of how deep you go. In such cases you have a choice of either staining the floor dark, replacing the damaged area or using a very strong bleach such as oxalic acid.

Related Q: I removed carpet from my 80 year old home and exposed oak flooring. We bought the house 50 years ago and have had carpet since then. In the high traffic areas there was a lot of dark sticky residue. When sanded these areas stayed darker than the rest of the floors. Early American stain was applied to a small area and dark areas look worse. Is there any way to lighten these stained areas?

A: You could treat it several times with oxalic acid which comes in crystal form, mixed with water. You should be able to buy this at a pharmacy. It should help.