Authors: Blake Ross, Extension Specialist, Agricultural Engineering, and Kathleen Parrott, Extension Specialist, Housing.
Publication Number 356-489, April 1998
Table 3. Hardness Classifications
| Concentration of Hardness | ||
|---|---|---|
| In Grains per Gallon (gpg) | In Milligrams per
Liter (mg/L) | Relative Hardness Level |
| Below 3.5 | Below 60 | Soft |
| 3.5 to 7.0 | 60 to 120 | Moderately Hard |
| 7.0 to 10.5 | 120 to 180 | Hard |
| 10.5 and above | 180 and above | Very Hard |
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