I live in an area with hard water - 17dH, 122mg/L Ca, 322ppm calcium carbonate.
I have had 6 axolotls for nearly 6 months and they seem to be fine with these water parameters.
Stability of conditions is important, and I have found that I have had to do more frequent water changes because the warm weather was causing an increase in evaporation, and increase in pH up to 8. I'm currently doing 20% water changes every other day to get everything closer to what comes out of the tap.