Water Hardness Table of Classifications
| 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 |
Table adapted from Water Treatment Fundamentals, prepared and distributed by the Water Quality Association
U.S. Geological Survey Water Hardness Explanation | Water Quality Association Scale Desposits from Hard Water
Water Hardness Map of the United States
Table adapted from and prepared by the United States Geological Survey
Water Hardness from Domestic Wells (2019)
Table adapted from and prepared by the United States Geological Survey
