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 Water Hardness Classifications

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