Calcium usually enters the water as either calcium carbonate -LRB- CaCO3 -RRB- , in the form of limestone and chalk , or calcium sulfate -LRB- CaSO4 -RRB- , in the form of other mineral deposits .

Calcium usually enters the water as either calcium carbonate -LRB- CaCO3 -RRB- in the form of limestone and chalk , or calcium sulfate -LRB- CaSO4 -RRB- in the form of several other mineral deposits .
