Originally Posted by mcmillcd
I second the magic eraser. If its truly a water stain I would use a mild acid cleaner like comet or something similar (of course test an inconspicuous area first) but most water stains are due to alkalinity and a mild acid with the magic eraser to get down in the grooves and cracks should do the trick.
Instead of comet, use a product called Bars Keeper. Is is less prone to scratching like comet it. It should be on the shelf next to or near the comet.
Regarding the magic eraser, just some water should be that is necessary. It is just that good.
And like mcmillcd said, test in an inconspicuous first regardless of what you try.