Equilibrium reaction- solubility of gypsum

the drinking water standards of 400 mg/L for Ca and 240 mg/L for S042 are exceeded by far. While the level for Ca is of rather technical significance, since high Ca values may lead to calcite precipitation in the pipe system (also see chapter 3.1.5.2), the sulfate standard has a medical background, because sulfate can cause diarrhea in high concentrations. 

To calculate the sulfate content, not only the S042 ion as listed in the species distribution but all S(6) species were considered. Most analytical methods determine all S(6) compounds as sulfate and, moreover, also the drinking water standard refers to this rather theoretical total sulfate content. 

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