| 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 |
Publication #: 356-489
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