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Basis of evaluation
Water analysis
Questions & answers
Ion exchange for dummies
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Basis of evaluation of your drinking water
The hardness of water
When water is referred to as "hard" this simply means, that it contains more calcium and magnesium minerals
than ordinary water. The degree of hardness of the water increases when more calcium and magnesium dissolves.
The total-hardness of water is measured in °dH (German hardness) and partitioned in three hardness scales:
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The hardness scale |
German degrees (°dH) |
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soft to reasonable hardness |
0 to 10 |
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medium hardness |
10 to 16 |
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hard |
more than 16 |
After a softening process the residual hardness should not be less than 8,4 °dH.
Chemical requirements
The following limiting values can be accepted as harmless for drinking water (recommendation WHO-EU):
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Chloride |
Objective value: 25 mg/l, Limiting value: 200 mg/l |
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Sulfate |
Objective value: 25 mg/l, Limiting value: 250 mg/l |
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Nitrate |
Objective- and Limiting value: 50 mg/l |
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Iron |
0,05 - 0,2 mg/l |
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