Our fireplace has a black concrete hearth. There are several white water stains on it that we would like to remove or cover. There is also a set of small dark hand prints on it. What can we do to restore the hearth to solid black? The home was constructed in 2007.

Was this a specially treated concrete, say concrete stained to look like black marble ?

There is no special effect--marble or otherwise. It is solid black. We don't know the contractor so don't know what kind of sealer was applied, if any.

Try wiping it it down with white vinegar. This is a very mild acid and you can work your way up to dilute Mureatic acid if you use gloves and ventilation.