Rudeofus suggested that I try tap-water. Here's the graph of the comparison of XTOL versus the concentrate, using a test-strip of TMY2. The XTOL was dissolved in distilled water, but the concentrate was dissolved in tap-water, so XTOL had an advantage.
The graphs are very close. Grain is the same, gauging in 22x loupes. My conclusion is: Tap-water had negligible effect.
Also, I saw no evidence of precipitate before or after development, and my water is hard. That's good news, but I'd like to learn more about dealing with dissolved minerals.
@Michael R: I'll confess that I've never tried 1+1 dilution before, so that graph is new to me. With that short toe, I can see why Tri-X is good for pushing.