If you have new water stains on your oak wood floors, you can get them out with a simple procedure that takes only a few minutes. When you see a new stain, immediately some mayonnaise on a paper towel and then place it face down on the water spot. Press the mayonnaise down into the floor and make sure that the entire area is covered with it.
Let the mayonnaise sit on the spot for a few hours or even as long as overnight, after which time you can lift up the paper towel, and then use a clean one to wipe up the excess mayonnaise.
If the initial coating dries out, reapply some more. The oil in the mayonnaise will have been absorbed through the finish displacing the moisture causing the stain mark and removed it from the flooring. For water stains that have been there for weeks or several months, you may have to resort to a more elaborate solution.