Salt-free softening guide

Water hardness is measured by the amount of calcium and magnesium minerals in water. Within the water quality improvement industry, Grains per gallon (gpg) is the most common method for designating the water hardness. Lab reports may express hardness using parts per million (ppm) or milligrams per liter (mg/L). Multiply the grains per gallon by 17.1 to get the equavalent ppm or milligrams per liter.

The Water Quality Association breaks down water hardness into the following categories:

  • Soft:   < 1 gpg   (<17.1 mg/L)

  • Slightly hard: 1 to 3.5 gpg (17.1 to 60 mg/L)

  • Moderately hard: 3.5 to 7.0

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