Calcium adds to water hardness and chloride accentuates maltness, sweetness and fullness. Typical concentratons for brewing water are 50 – 150 ppm Ca2+ and 50 – 150 ppm Cl- . It is also used to lower the mash pH. Additons can be put in the brewing water or directly into the mash.
Calculatng how much salt to add depends on the mineral levels already in soluton. Contact your local water supplier for informaton on Ca2+, Mg2+, CO32-, SO42- and Cl- in your municipal water.
For your information: This product is also used in pickling fruit and vegetables and it makes picked products crisper. Some more information can be found here: http://www.healthycanning.com/calcium-chloride/