Water Hardness
The concentration of calcium and magnesium dissolved in water; it is expressed in mg/l of CaCO₃ or in French (ºHF), German (ºdH) or English (ºe) degrees.
Hardness comes from the minerals that water dissolves as it passes through the ground, so it varies greatly from one area to another. The most commonly used equivalences are: 1 ºHF = 10 mg/l of CaCO₃; 1 ºdH ≈ 1.78 ºHF; 1 ºe ≈ 1.43 ºHF. It is measured with test strips, with drop titration kits or in the laboratory, by EDTA titration (ISO 6059).
In cleaning, hardness has two effects. On the one hand, calcium and magnesium react with part of the surfactants and reduce their effectiveness, so more product is needed. On the other, when the water is heated they precipitate as calcium carbonate and form limescale on heating elements, pipes, machines, tableware and glassware. It is controlled in three ways: with a water softener or reverse osmosis upstream of the equipment, with detergents containing enough sequestrants for the local hardness and, once limescale has formed, with acid descalers. That is why data sheets for machine detergents state the hardness up to which they can be used.
Instaquim dishwasher detergents with a maximum hardness stated in their technical data sheet (dose of 1-5 g/l, except Supersol, 2-5 g/l, at 55-60 ºC):
- Deternet (pH 1 %: 12.5): soft water, up to 20 ºHF.
- Deterdur (pH 1 %: 12.5): up to 40 ºHF.
- Supersol (chlorinated granules, pH 1 %: 11.5): up to 45 ºHF.
- Deterplus (pH 1 %: 12.5): very hard water, up to 65 ºHF.
In laundry, Duron (pH 1 %: 11.5; 10-12 g per kg of dry laundry) can be used in water of up to 60 ºHF, according to its data sheet.
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