[pushkins]

Both answers are correct, tho water usually causes more of an opaque discoloration to happen. (sorta looks like an oil stain a blackish/blueish color)

Make sure the stain is isolated by itself, if it comes from under a cabinet or near the toilet or shower then further investigation would be required. Usually if it is a water related problem the stain would tend to "grow" as it is exposed more and more.