G'day,
It really depends on what the finish is, but I have had success in the past by rubbing a cloth that is
slightly dampened with denatured alcohol, ie the alcohol evaporates almost immediately from the surface. This actually dissolves the very top of the finish and helps to remove the water mark. Obviously this only works on finishes that are dissolved by alcohol :D
Do a search in the forum for "moisture marks" or "water rings" as there have been a few threads on this over the years. Here is one
http://www.woodworkforums.ubeaut.com...ad.php?t=13867
Cheers,
Oz Man