||Gypsum (Calcium Sulphate) is the inorganic compound with the formula CaSO4 that adds hardness to soft brewing water. Chemically, gypsum rock is calcium sulfate with two molecules of water. Gypsum rock is found throughout the world and deposits in North America run from Baja, Mexico, through Utah and from southwestern Texas to the Niagara River in New York State. Brewers that use distilled or filtered water like to add some gypsum back into the water to give it some hardness. Gypsum can also be used to lower the pH of water.