Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers


Total Hardness

Reviewed by Raghvendra GopalCheckmark
Last updated: June 1, 2021

What Does Total Hardness Mean?

Total hardness is a measurement of the mineral content in a water sample that is irreversible by boiling.
More specifically, total hardness is determined by the concentration of multivalent cations in water. These cations have a positive charge that is higher than 1+. Typically, cations have a charge of 2+. The most common cations present in hard water are Mg2+ and Ca+.

Hard water is not seriously harmful to human health. However, water with a high level of hardness could cause serious problems in industrial settings, where water hardness is typically monitored to prevent costly failures in components like cooling towers, boilers and other equipment that contain or process water.

High total hardness can result in abnormal cloudiness and the formation of scale. However, levels of hardness that are too low could make the water corrosive and more aggressive. Thus, industries that use equipment and machinery that handle water should ensure that the total hardness levels are maintained at appropriate levels to prevent the water from becoming corrosive.


Corrosionpedia Explains Total Hardness

Although hardness is mostly caused by the dissolved mineral compounds calcium and magnesium, other ions such as iron and manganese may also contribute to hardness in small amounts. As calcium carbonate, hardness is measured in milligrams per litre (mg/L) or grains per gallon (gpg). The equation Hardness = 2.497 (Ca) + 4.118 is used to measure hardness (Mg). As a result, changes in the magnesium pool have a greater impact on hardness than changes in the calcium pool.

Various measures and kits can be used to measure the magnesium and calcium present in hard water. These two essential minerals are the main cause of water hardness. Water systems that use underground water as a source are more concerned with water hardness, since as water moves through rock and soil it dissolves small amounts of naturally occurring minerals, carrying them into the groundwater supply. Water is a good solvent for calcium and magnesium, so when the minerals are present in the soil around a water-supply well, it results in hard water. To reduce the total hardness of water, certain processes such as water softening can help. With softening, the adverse effects of hard water can be reduced significantly.

Calcium and magnesium, the two key components of hardness, are potentially beneficial to humans. Many countries include guidelines on the amount of such minerals that should be present in drinking water.


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