yes your water could be too hard so instead i would use some distilled water instead of tap. (a gallon for under a buck at most store)so you're sayin my water is too hard for henna? hmm... what if i do a "henna wash"-mix henna w/ a chelating poo? do a good steam dc afterward?
(dumb i know, just throwin somethin out there
Also make sure that the water you use is not HOT HOT or boiled. This can make the henna harden your hair.