Since they give me the hardness, that should contain the total calcium and magnesium. I was reading on braukaiser that generally 70% of this hardness comes from calcium. So 30% (or 19.2 mg/L) should be the magnesium content. That would mean 44.8 would be calcium. But since calcium is listed already (13.9), do I add the 44.8 to 13.9, or is should I subtract the 13.9 from the 64.1 to get 50.2 for the magnesium? Ultimately I am wondering what numbers I need to put in a water calculator.
Unfortunately, that generalization isn't worth much. The amount of calcium or magnesium CANNOT be generalized since it is totally dependent upon the minerals the water contacted on its way to your tap. A 70/30 split between Ca and Mg may be correct in some waters, but more than likely, its not.
If the hardness and calcium values from the water report are correct, then the magnesium content is more like 7 ppm.
It's sad to see misinformation like that on the web...but it does exist.