Deals with the basics of analysis of water and wastewater samples for pH, Acidity, Alkalinity and Hardness. It also talks about indirect methods of calculations of different types of alkalinties, harnesses and acidities.In Hardness estimation the major substances in water is 

Calcium carbonate and magnesium carbonate. The ammonia and 

ammonium chloride buffer pH is 10. At the particular pH it 

will form the complex with both calcium and magnesium. So 

the titre value gives the total hardness of the solution.

If you want to measure calcium alone instead of adding pH 

10 buffers add pH 12 buffer (1M NaoH).

I think calcium carbonate is insoluble in water.