Neither calcium nor magnesium are unsafe at normal concentrations ,<70mg/L. Although at high concentrations, >100mg/L, they can have an impact on the taste of the water. Sensitive groups, e.g. people who suffer from kidney or gall-bladder stones are likely to notice an increase in stones if they regularly intake water with calcium concentrations of 150mg/L or more. Magnesium from concentrations of 70mg/L and above can cause infants to get diarrhoea. Diarrhoea becomes a general concern for all consumers once the concentration exceeds 300mg/L, but at this concentration the water is extremely bitter and it is highly unlikely that it will be consumed by an average user. Thus Calcium and Magnesium should be tested, at least initially, to get a baseline. If they are of low concentrations, then it is unlikely they will be problematic.
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Thanks Juan for your detailed response!
Calcium and Magnesium should be tested, however, routine testing add to cost.
Thanks Uday, I don't think routine monitoring for Ca or Mg would be required if the baseline test showed both at low concentrations. Unless the water source is regularly impacted from external sources. Most Labs measure Ca and Mg to calculated the Total Hardness anyway e.g. T.H. = [2.497 x calcium (mg/l)] + [4.118 x magnesium (mg/l)] from a local South African example, so if total hardness is below 300mg/L then Ca and Mg are likely at safe concentrations.