KH is SURE NOT AN UNIT OF MEASURING HARDNESS !!!
KH is usually called "temporary hardness" or "Carbonate Hardness" or "Alkalinity". But KH is really a mesurement of the capacity for water to neutralize an acid. The higher the KH, the harder for the pH to be changed.
*** If referring for Hard/Soft water, the right measuring unit is GH, usually called the "General hardness" or "Total hardness". GH is a unit to measure all the dissolved salts in the water, mainly calcium(Ca) and magnesium(Mg).
If you want soft water, the GH of your water should be lower than 60mg/L CaCo3