Maintaining a natural wood floor such as oak can be a bit of a challenge. You need to deal with damage and water spills right away or your floor could have permanent damage. If you don't get to a water spill immediately, it could cause a dark water spot on your oak flooring. If this happens, try not to panic. You may be able to restore your floor and get those water stains out.
Rub the water stains on your oak flooring using No. 2 steel wool. This should help rub out a lot of the stain.
Clean the area thoroughly with a wood floor cleaner.
Soak the area in vinegar and let it sit on the water stain for several minutes. If you still see the water spot, repeat the vinegar application.
Put on a pair of gloves to protect your hands.
Create a solution of 29.6ml. oxalic acid to 1 qt. of water if the water stain is still present. Apply this solution, and use a towel to rub it into the stain.
Clean the area with a regular floor cleaner to remove the oxalic acid solution.
If cleaning the water stain doesn't work, you may need to sand the area with a fine sandpaper before re-waxing and polishing the spot on your oak flooring.
Wear gloves when working with oxalic acid.