The presence of combinations of these minerals is most commonly measured as total alkalinity, total hardness, pH, iron, manganese, and total dissolved solids. Alkaline waters usually have high bicarbonates that allow the water to receive acid without reducing the pH. These waters are not appropriate for certain processes that require low alkalinity water, such as mineral water or beer. The presence of calcium and manganese dissolved in water give water its hardness. If hardness is due to bicarbonates of magnesium and calcium it is called temporary hardness because much of it precipitates on heating, forming scale in the water system. Permanent hardness is due to the presence of sulfates, chlorides, and nitrates of these elements.
Hard water causes toughening of the vegetable skin during blanching and canning.
Soap and alkaline detergents produce scum, curd, or deposits making washing operations more difficult. Usually, hard water must be softened to be acceptable for food and beverage processing. The most common water softening processes are precipitation, cation exchange, and demineralization. Precipitation and cation exchange or a combination of both are the most widely used methods in the water industry. When iron and manganese are oxidized, they produce dark precipitates that stain and discolor equipment and fixtures and sometimes cause unpleasant odors.