When people speak of soft water, I have heard everything from 0 to 7 grains of calcium carbonate /gal (gpg). The official definition is below. Water hardness is classified by the U.S. Department of Interior and the Water Quality Association as
Units are grains of calcium carbonate /gal (gpg)
Soft water = 0 – 1
Slightly Hard = 1 – 3.5
Moderately Hard = 3.5 – 7.0
Hard 7.0 – 10.5
Very Hard over 10.5

Soft water is 1 gpg or less.

The grains per gallon comes from 7000 grains of wheat / pound. To convert from gpg to ppm (parts per million), multiply gpg x 17.1. such as 10 gpg = 171 ppm calcium carbonate.

To learn more call or text 720-802-2057 (303-How-Pure)
Kind Regards, Mike