I know that this is a very old post and won't help the original poster, but for anyone researching, water alone can etch marble because many water sources are on the acidic side. Your teeth and their condition are much more important than any countertop surface. Use an anti-cavity toothpaste and then use trays on top of marble to place items used frequently to help protect the surface. Use a marble cleaner and not water to clean the surface for the best outcome. Keep the marble sealed.