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|
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.
See more examples here.