Calcium Significance to Humans
The human body requires approximately 0.7 to 2.0 grams of calcium per day as a food element. This amount is considerably greater than the calcium concentration of normally consumed quantities of even hard water. Concentrations of up to 1,800 mg/L of calcium in drinking water have been reported to be harmless.
Calcium in water also reduces the toxicity of many chemical compounds to fish and other aquatic fauna. For example, mature fish that have been killed by 0.1 mg/L of lead in water containing only 1 mg/L of calcium have not been harmed by this amount of lead in water containing 50 mg/L of calcium. A concentration of 50 mg/L of calcium has been observed to cancel the toxic effect upon some fish of 2 mg/L of zinc, 0.7 mg/L of lead and 10 mg/L of lead.