Hardness comes from the calcium (Ca²⁺) and magnesium (Mg²⁺) ions that water dissolves as it passes through limestone and dolomite rocks underground. When heated, bicarbonates turn into carbonates and precipitate; this is the scale found in boilers, water heaters and machines.
Units
| Unit | Equivalent |
|---|---|
| 1 °fH (French) | 10 ppm CaCO₃ |
| 1 °dH (German) | 17.8 ppm CaCO₃ |
| 1 °e (English) | 14.3 ppm CaCO₃ |
Classification (ppm CaCO₃)
- 0–60 soft
- 60–120 moderately hard
- 120–180 hard
- >180 very hard
Hardness is removed by ion exchange softening. You can use our calculator to convert between units.
