In the UK, The Water Supply (Water Quality) Regulations 2016 in England & Wales, published by The Drinking Water Inspectorate, allows for a concentration of sodium of up to a maximum level of 200mg/l in water supplied to a property. Very hard water up to 400mg/l hardness would still be considered wholesome after softening.

The answer depends on if there is a chance that the softened water will be consumed either by those on low sodium diets or by babies drinking formula milk made up from the water.