I have hard water.
live in indiana. lime from all the limestone that is everywhere.
B & M, especially excelsior based!
camo
I recall in an interview that tolerance of very hard water was one of Will's design goals for Excelsior. If memory serves he tested the base during development with a wide range of waters, from distilled to very hard to sea water, to make sure it would lather in everything.
I'm 3017ing through a jar of Clusterfig in the Excelsior base currently, and it certainly is an excellent performer, though in my relatively soft water it's not clearly better than any of the other top-tier soaps in my den.