Water analyses are conventionally expressed, for both cations and anions, in parts per million by weight (ppmw) except for hardness and alkalinity which are usually expressed in ppmw of calcium carbonate (CaCO3). These ppmw values can be converted to a common basis (such as milli-equivalents/liter) by dividing by the equivalent weight of the ion and multiplying by the specific gravity of the water solution. This permits the summation of oppositely-charged ions such that total cations will then equal total anions. Cation and anion concentrations in milli-equivalents/liter can be converted to ppmw CaCO3 by multiplying by the equivalent weight of CaCO3 (100.08/2 = 50.04) and dividing by the specific gravity of the water solution.
Total hardness is the sum of calcium and magnesium and is therefore equal to 334 ppmw as CaCO3 (250 + 84). Correspondingly, alkalinity is the sum of CO3–2, HCO3–1, and OH–1 ions and is equal to 300 ppmw as CaCO3.
Total hardness is the sum of calcium and magnesium and is therefore equal to 334 ppmw as CaCO3 (250 + 84). Correspondingly, alkalinity is the sum of CO3–2, HCO3–1, and OH–1 ions and is equal to 300 ppmw as CaCO3.