Hard waters are as satisfactory for human consumption as soft waters, however, because they require considerable amounts of soap to produce a lather and produce scale in hot-water pipes, heaters, etc. they are often not desirable for a household.

The hardness of waters are commonly classified as follows:

mg/L	Degree of Hardness
0 - 75	Soft
75 - 150	Moderately Hard
150 - 300	Hard
300 and up	Very Hard

The calculation of the hardness caused by each ion is performed by the following equation:

Hardness (in mg/L) as CaCO₃ = M²⁺ (mg/L) x (100 g/mol CaCO₃/ atomic weight of M²⁺⁾    

The following calculator determines the hardness of waters based on the concentrations of the divalent cations Ca, Mg, Mn, Fe and Sr.

HARDNESS CALCULATOR 

Concentration

Ca²⁺      mg/L mol/L

Mg²⁺      mg/l mol/l

Fe²⁺       mg/l mol/l

Sr²⁺       mg/l mol/l

Mn²⁺       mg/l mol/l

*a value must entered in each field (i.e. if none present, enter 0)*

 

Hardness

as mg/L of CaCO3