Soft and Hard Water

The U.S. Geological Survey recommends the following classification into hard and soft water (based on Total Hardness TH):

Water Type TH in ppm CaCO3 TH in °dH TH in mM TH in meq/L
soft < 60 < 3.35 < 0.6 < 1.2
moderately hard 60  to  120 3.35  to  6.7 0.6  to  1.2 1.2  to  2.4
hard 120  to  180 6.7  to  10.05 1.2  to  1.8 2.4  to  3.6
very hard > 180 > 10.05 > 1.8 > 3.6

aqion water hardness output

This classification is used by aqion to categorize aqueous solutions into four water types. One example of a moderately hard water is shown in the right screen shot.

[last modified: 2015-08-09]