Water hardness is built up from two main groups: calcium hardness + magnesium hardness.
Calcium hardness is best described by the natural occurring salts of calcium, which are: calcite and gypsum, calcium carbonate: (CaCO3) and calcium sulfate (CaSO4) respectively.
Magnesium hardness consists of magnesite: magnesium carbonate (MgCO3).
So the question is if these salts may interfere with the Halamid Ion in water. In water, there is a tendency to form badly or insoluble salts, which calcium carbonate, calcium sulfate, magnesium carbonate in principle are. There would be little propensity to form salts with Halamid especially not in the concentrations used. This behaviour was confirmed by laboratory tests (ref 957) in which Halamid was tested on its efficacy on bacteria under soft to hard water hardness conditions. The efficacy was exactly the same for all degrees hardness.
If desired, water hardness may be combatted by the use of common complexing agents like EDTA, DTPA and NTA. We do warn to carefuly check the pH when adding complexing agents which are often added in their acidic form. pH below 7 may cause the Halamid solution to destabilize.