black galaxy granite headstone

Hello,
 
i found this site,  findstone.com, and have read through some of the Q&A's. But i did not see anything  specific to the care of granite, when it is used, not as a counter top, but as a headstone.
i tragically lost my 18 1/2 year old son on October 5th, 2008, due to the hazing rituals associated with fraternities, and after careful consideration, i decided on the 'black galaxy' granite, had it formed into a 3-part bench,  and it came from India.
the stone was installed in Tucson Arizona, and this is a very dry climate. however the cemetery where my son is buried, waters the grass, at the least, in his section, every other day with well water, which leaves horrid water spots on the stone.
as of now, my sister and i re-wet the stone, then polish till our arms are ready to fall off, only to still have spots. i was told by some to 'not put any compound on the stone as it is living' and by others 'that it was ok to seal the stone' i am beyond confused about the care of the stone. i intend to take care of it for a long time to come, and want it to retain its beauty throughout time.
i would really appreciate any help that you  would be willing to share.

please reply one way or the other i really need the help

Thank you all so much
Stacy