Meaning of the total hardness of water

What is the total hardness of water?

Calcium and magnesium-total hardness







Calcium and magnesium make up the majority of what is known as total water hardness

Technically, other multivalent cations (of valence greater than +1) are considered part of the hardness. However, its concentration is usually negligible in relation to that of calcium and magnesium.

The hardness of a water can be determined by titration, which is practical, cheap and simple. Inexpensive kits are sold to carry out this analysis.

To the hardness that only the Ca+2 it is called calcium hardness or calcium. To which the Mg+2, it is called magnesium hardness. The sum of both is known as total hardness.

Both calcium, magnesium and total hardness are expressed in units of mEq / L or mg as Thief3/ L. 

The terms hardness and hard water They are due to the way multivalent cations, such as calcium and magnesium, attract and bind to the natural oils in the skin, leaving it with a stiff feeling.

In addition to the above, a hard water: 

  • Leaves hair stiff.
  • Causes a characteristic taste (not pleasant for most) in drinking water.
  • It forms precipitation that encrusts or clogs water pipes and equipment such as heaters, irons, and appliances. These precipitations increase when the water warms up.
  • The positive charges in the hardness cause it to bind to phosphates, which are strongly anionic. Since the action of most detergents is dependent on phosphates or other anionic surfactants, the hardness decreases their effectiveness. 
  • Hardness is also a problem for reverse osmosis equipment, due to its insolubility when the concentrations of bicarbonates, carbonates, sulfates, fluorides or silicates are appreciable.

Approach to pipes affected by mineral encrustation due to encrusting water.

Figure 1. Approach to pipes affected by the incrustation of minerals due to water with a high concentration of hardness.

Unit conversion, mg / L to mg Thief3/ L






Ca concentration+2 in certain water is 17 mg / L and the concentration of Mg+2  it is 8 mg / L. Express both concentrations in mg CaCO3/ L and report the total hardness of this water in mg CaCO3/ L.







Unit conversion, mg / L to mg Thief3/ L




Applying this to the previous example:







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