Water hardness table
Level Type Water hardness
°dH °T.H. mmol/l Clarke
1soft 0-7 0-15 0-1.5 0-9
2medium 8-14 16-25 1.6-2.5 10-16
3hard 15-21 26 -37 2.6-3.7 17-25
4very hard > 21 > 37 >3.7 >25
20