Could a Knight of the Cross make holy water, then? If so, why does Michael never make any for Harry? Or did Harry just ask Father Forthill to make it for him before he'd met Michael?
Harry didn't really need it before he met Michael. Harry has said before that he asked Father Forthill for a big batch of it after the war with the Vampires broke out. I suspect a Knight
could make it (I mean, just use the Holy Stirring Stick that is one of the swords and you've got insta-Holy) if he
believed it was okay to do. But I imagine, if asked, the various book Knights would answer:
Michael - "That's really not my place, Harry. I'm not one of the clergy."
Sanya - "I am Agnostic. How would I make water 'holy'?"
Shiro - "Oh, no, I am sorry, but I am not a priest."
I've had a few Champion-of-God type players create Holy Water on the fly. Always as a Maneuver.