Hardness of Water

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Hardness of Water


the aggregate of properties caused by Ca2+ and Mg2+ ions contained in water. The total concentration of Ca2+ ions (calcium hardness) and Mg2+ ions (magnesium hardness) is the total water hardness. A distinction is made between carbonate and noncarbonate hardness. The carbonate hardness corresponds to that part of the Ca2+ and Mg2+ ions that is equivalent to the bicarbonate HCO3 ions in the water. In the USSR the hardness of natural waters is expressed in milligram equivalents per liter, and the hardness of softened or desalinized water is expressed in microgram equivalents per kilogram. Until 1952 the hardness of water in the USSR was expressed in degrees (1° equaled 0.357 microgram equivalent per liter).

The hardness of natural waters varies within very wide limits, from 0.1–0.2 milligram equivalent per liter for river and lake waters in taiga and tundra zones to 80–100 milli-grams equivalent per liter for some underground water and for sea and ocean waters. The increased hardness of natural sources is mainly due to contact of the water with rocks containing calcium and magnesium carbonates and sulfates. Hard water cannot be used in heat and power engineering or the manufacture of artificial fibers. The use of hard water leads to increased formation of scale in boilers and heating equipment, which interferes with heat exchange. In laundering, water hardness raises soap consumption, since part of the soap forms an insoluble precipitate with Ca2+ ions. Vegetables and meat boil badly in hard water, since Ca2+ ions yield insoluble compounds with the proteins of food products. Hard water also spoils the taste of tea. Great hardness promotes the formation of urinary calculi in humans. The permissible limit of hardness for central water supplies is 7 milligrams equivalent per liter; in exceptional cases, with the consent of health supervisory bodies, it can be higher (up to 14 milligrams equivalent per liter). If a source of very hard water must be used, special methods of softening are used.


Gigienicheskoe normirovanie solevogo sostava pit’evoi vody. Edited by S. N. Cherkinskii. Moscow, 1963.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Minor contributors to the total hardness of water include other polyvalent ions, such as aluminum, barium, iron, manganese, strontium, and zinc.
DETERMINATION OF HARDNESS OF WATER. World Health Organization; 1999.
Firstly, the alternative liming blend of [Na.sub.2]C[O.sub.3] plus Ca[Cl.sub.2] is capable to simultaneously increase the alkalinity and hardness of water as well as the CaC[O.sub.3].
On the other hand, it is assumed that hardness of water higher than its alkalinity (CH/TA ratio > 1) is harmless to fish growth (BOYD, 1979).
The pH, ammonia concentration, level of microbial contamination and the hardness of water used in scald tanks, washers and chiller tanks can influence the ability of sanitizing procedures to remove microorganisms from carcasses during processing.
Tables I A & B gives the analytical results for the concentrations of calcium, magnesium and hardness of water (the sum of the concentrations of calcium and magnesium) for each sample according to the location site number shown in Figure 1.
Carbonates and bicarbonates are source of ordinary hardness of water while chlorides and sulfates cause permanent hardness.
The studies on the influence of the high hardness of water and the water containing the sodium and chloride ions on the pregnant animals' body have not been found by us.
The phytoplankton showed a direct relationship with light penetration, pH, oxygen, total alkalinity and total hardness of water (Mahboob, 1986).
For example, if the initial calcium hardness of water is 50.0 mg [L.sup.-1] CaC[O.sub.3] and it is desired to produce calcium-free water (x = 0), the probable application rate of reagent grade Na-EDTA needed is equal to 3.3628 * 50.0 or 168.1 mg [L.sup.-1].