An accidental circular water stain once (dis)graced this end table. My wife looked up how to remedy that and found a very surprising answer: mayonnaise. She squirted some on the stain and rubbed it in with her fingers, then repeated that a couple hours later. Stain ... gone! Mayo is made mainly from oil (e.g. canola, avocado, safflower, etc.) which seeps into the finish and displaces the moisture. More techniques for removing water stains can be found in this Bob Villa article.