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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

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

Map of Water Hardness Areas in the United States

Table adapted from and prepared by the United States Geological Survey

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