Calcium ( Ca2+ ) and Magnesium ( Mg2+ ) are present in crystalline and sedimentary rocks ( calcite CaCO3 ), dolomite ( CaMgCO3 ), magnesite ( MgCO3 ), Gypsum ( CaSO4 ), apatite ( Ca5(PO4)3 ), fluorite ( CaF ), plus sandstone and detrial rocks with carbonated cement ); they are very soluble substances, present in most type of water.

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Their concentration and the Ca/Mg ratio provide information about the origin of the water and the nature of the reservoir.

 

The calcium ion is sensitive to base-exchange phenomena.

 

Total hardness is the concentration of Ca2+ and Mg2+.

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Carbonated hardness is the concentration of bicarbonate/carbonate ( HCo3-, CO32- ).

 

Due to its laxative effect, the French AEP Standard upper limit for Mg is 50 mg/l.

No AEP Standard exists for Ca.