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Water Hardness Areas in the United States


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



Map of Water Hardness Areas in the United States
Map taken from Water Treatment Fundamentals, prepared and distributed by the Water Quality Association