Reduction in Alkalinity
While "temporary hardness" can be removed by boiling the water, it is seldom used on a commercial scale because of the costs associated with heating the water.
The addition of calcium hydroxide-slaked lime or hydrated lime can be used to reduce the level of calcium, magnesium, and sodium salts of carbonates and bicarbonates in the water. Where calcium and magnesium are primarily in chloride or sulfate compounds, this treatment is noticeably less effective.
Food Grade Acids
Alkalinity can be reduced by additions of food grade acids (sulfuric, hydrochloric, phosphoric), but sometimes citric and lactic acids can be used too. In theory, sulfuric and hydrochloric acids can be used, but most brewers do not want to add excess sulfate or chloride ions to their mashes because of potential flavor effects.
In Germany and in other countries where mineral acids (i.e., food grade acids) are prohibited, pH reduction can be achieved by using carbon dioxide. Carbon dioxide is introduced into the high pH water by means of a diffuser, which is typically installed in an existing pressurized pipe or at the bottom of a tank
Click on the following topics for more information on brewing water.