Water hardness is caused by dissolved salts of alkaline earth metals, mainly calcium and magnesium. The properties of hard and soft water affect both human health and technological processes in production in different ways.
Hardness is a feature of the physical and chemical properties of water due to the presence of dissolved salts of alkaline earth metals. The main contribution to hardness salts is provided by calcium and magnesium, although other metals may also be present in small amounts: manganese, iron, including trivalent, strontium, barium, aluminum.
There are 2 types of hardness: temporary, caused by hydrocarbons and carbonates, and permanent, caused by chlorides, sulfates and silicates of calcium and magnesium. Temporary hardness is almost completely eliminated by heating the water to precipitate calcium carbonate and magnesium hydroxide. Constant hardness is controlled using reagent methods (eg lime-soda) or ion exchange methods.
Measures and limits of water hardness
The hardness of natural water varies widely. These changes depend on the intensity of the processes of dissolution and weathering of rocks, such as limestone, dolomite, gypsum, within watersheds and water sources. The source of ions can be microbiological processes in the soils of the catchment area and in bottom sediments, as well as wastewater from various enterprises.
The hardness of natural water is strongly influenced by seasonal climatic factors such as evaporation, melting of snow and ice, precipitation. The least hardness of surface waters is observed in spring.
The content of calcium ions decreases with an increase in water mineralization and usually does not exceed 1 g / l. Magnesium ions can accumulate and, in highly mineralized waters, their amount can be several grams or, in salt lakes, tens of grams per liter. In seas and oceans, water hardness is very high.
The measured total concentration of calcium and magnesium cations serves as a numerical expression for water hardness. In world practice, several units of water hardness are used, for example, mole per cubic meter. In Russia, on January 1, 2005, a new national standard was introduced, according to which the hardness of water is measured in degrees of hardness.
Influence of water hardness on human life
The World Health Organization does not establish any criteria for the effect of hardness of drinking water on human health. Although some studies have noted a decrease in cardiovascular disease when drinking hard water. The constant use of soft water can lead to an imbalance of minerals in the human body, because up to 15% of the daily intake of calcium a person receives from drinking water. The body's need for magnesium is replenished in the same way.
The interaction of hardness salts with detergents destroys the natural fatty film on human skin and clogs pores. Increased hardness degrades the quality of the water and can impart a bitter taste to it. Hardness salts also form insoluble compounds with food proteins when meat, fish and vegetables are cooked, which impairs the cooking process.
Water hardness contributes to the formation of scale during heating, which reduces the intensity of heat exchange in heating systems and leads to excessive consumption of fuel. Excessively soft water, in turn, causes increased corrosion of water pipes.
