[albertapro]

Ive never tried but ive read from serveral sources:

Mix equal parts of water and white vinegar in a bowl, using enough to clean the surface that has the calcium issue. The vinegar alone is acidic, but by diluting it with the water mixture you now make the mixture safe for use on the granite while still keeping it strong enough to remove the calcium buildup.

Dip the edge of a cleaning rag into the mixture and wipe it over your granite surface. Repeat as needed until you remove all calcium residue.

Rinse the cloth with water, wring out and wipe it over the granite again to remove any remaining vinegar mixture.

Dry the surface with a clean rag, and also dry the granite each time you use or notice water spot development on the granite surface.