The hardness of water is the number of ions of calcium Са2+ and magnesium Mg2+dissolved in water.
The most widespread problem regarding water quality is its hardness. At first, the term ‘hard’ was used for water that made washing up difficult.
The main source of calcium and magnesium salts in water is washed out by natural water deposits of limestone, plaster stones and dolomites.
In low-mineralized waters calcium ions present the highest content. With an increase in mineralization the content of calcium quickly declines, and rarely exceeds 1 g/L. The content of magnesium in mineralized waters can reach several grams, and tens of grams in salted waters.
Calcium ions and magnesium ions do not harm any living organisms, but their content in water in large volumes is not advisable because such water is not appropriate for domestic purposes.
Hard water significantly increases consumption of soap and detergents during washing up, boils soft meat and vegetables slowly, slows down gastric motor activity. It is not suitable for water supply systems and feeding water heating appliances.Hardness is measured in milligrams equivalent per liter (meq/L). Industrial standards on the acceptable level of hardness depend on the type of equipment used. They usually consider water with a hardness exceeding 1 meq/L as being hard.