One way to remove white water stains from wood is to use an hot iron on a smoothly-textured, lint-free cloth placed over the stain, iron very briefly (seconds), lift the cloth, and repeat until stain is gone. No steam irons!
If it's to deep, only sunshine and time will minumize it, then it's time to refinish it.
If it's to deep, only sunshine and time will minumize it, then it's time to refinish it.