LaMotte Water Analysis Kit for Home Brewers - Manual (Page 9)

Since water has a neutral charge, the total number of negatively charged
anions must equal the total number of positively charged cations. Six ions
typically make up 98% of the total ions so the sodium concentration can be
estimated by testing for the fi ve other ions.
Negative Ions
Chloride (ppm) + Sulfate (ppm) + Alkalinity (ppm as CaCO
3
) = A
35 48 50
Positive Ions
Total Hardness (ppm as CaCO
3
) = B
50
Sodium (ppm) = (A – B) X 23
SODIUM (by calculation)
NOTE: The Total Hardness result incorporates two ions - calcium hardness
and magnesium hardness.