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Water hardness table
Level
Type
1
soft
2
medium
3
hard
4
very hard
Water hardness
°dH
°T.H.
0-7
0-15
8-14
16-25
15-21
26-37
> 21
> 37
ENGLISH
mmol/l
Clarke
0-1.5
0-9
1.6-2.5
10-16
2.6-3.7
17-25
>3.7
>25
21