Originated From GMC Trade Secrets
Are you sure it's water? I don't think I ever saw a water stain on marble?
You can buy refinishing kits at most hardware and big box stores. It takes a little elbow grease, but it's relatively easy to polish the rings or spots. You should refinish counter tops every couple of years anyway. It will bring the original golss back to the countertops.
Marble needs to be polished to remove flaws, I doubt you have the right equipment.
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Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them