well, different brand, different mix. for example
a 50-lb bag of Kerabond takes 1-1/2 gal of water
a 50-lb bag of PremiumPlus? how about 2-1/2 gal.
that's right, I had to double-check to be sure, but that's what the bags say. I've used both and have to say both seem to work.
Both are considered "premium" dry-set mortars, but big diff in water needed. Why? I have no idea, but it's there.