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Water Hardness Map of the United States

Water Hardness Table of Classifications

Water Hardness Table


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



Water Hardness Map of the United States

Water Hardness Map of the United States
Table adapted from and prepared by the United States Geological Survey







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