Hardness, or the quantity that expresses the total content of calcium and magnesium carbonates present in the water, is expressed in French degrees (° F): 1 ° F (French degree) corresponds to 10 mg/l of calcium carbonate. Based on the hardness, the waters can be divided into:
> 35 ° F very hard waters; > 350 mg/L
22 – 35 ° F hard water; 220-350 mg/L
15 – 22 ° F medium hard water; 150-220 mg/L
7 – 15 ° F fresh water; 70-150 mg/L
0 – 7 ° F very soft water. 0-70 mg/L
The Legislative Decree no. 31 of 2001 defines water with hardness between 15 and 50 ° f as drinkable.