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Water Hardness
| grains per gallon (gpg) |
milligrams per liter (mg/L) parts per million (ppm) |
U.S. Geological Survey Classification |
Water Quality Association Classification |
| < 1.0 | < 17.1 | soft | soft |
| 1 to 3.5 | 17.1 to 60 | soft | slightly hard |
| 3.5 to 7.0 | 60 - 120 | moderately hard | moderately hard |
| 7.0 to 10.5 | 120 - 180 | hard | hard |
| 10.5 + | 180 and over | very hard | very hard |
