Used in beer making as a water treatment. Gypsum increases hardness and lowers pH. Its use is known to increase the perception of hop flavor compounds in beer. Used in winemaking to lower the pH of the must. As calcium sulfate is not removed from water by boiling, when present, it is referred to as permanent hardness.
Usage varies depending upon your exact water profile. Additions can range significantly based off your water source. Usage below is something fairly typcial for many tap waters.
Chemical name: Calcium Sulfate (CaSO4)