What value should the residual hardness be set to?

Table of Contents

• Soft water is corrosive
• Does softening change the pH value?
• The sodium content increases
• Salt consumption is increasing
• Conclusion

There are a few theories about how to adjust the residual hardness. It is often claimed that soft water is dangerous for the pipes and that the residual hardness should not be set lower than 8 °dH. With this article we would like to shed some light into the darkness.

Soft water is corrosive

It is often said that soft water is corrosive. This claim is completely true, but what is not mentioned is that water is always corrosive regardless of whether it is soft or hard. Corrosion occurs when a substance (often metal) reacts with oxygen. Since water always contains oxygen (H2O) by definition, it can corrode when combined with metal. The problem with corrosion affects, for example, copper and galvanized steel pipes (rust or verdigris can occur). This danger does not exist with plastic pipes. If you have problems with corrosion of pipes (for example pipe bursts), you should think about installing a dosing system regardless of installing a softening system.

Does softening change the pH value?

Our softening systems work with the neutral exchange process. Calcium and magnesium ions are exchanged for sodium ions. The pH value does not change! There are of course other processes such as the reverse osmosis technique. When softening by reverse osmosis, the pH value changes downwards and the water becomes slightly acidic. However, we do not use this procedure in private households. Therefore, there is no reason against low water hardness here either.

The sodium content increases

For example, sodium is a component of table salt (NaCl) and a natural component in water. As already mentioned before, during neutral exchange (or ion exchange) the sodium content increases by approx. 8 mg per liter and per °dH removed. So if you previously had a water hardness of 20 °dH, then after softening you will have 160 (20 x 8) mg per liter more sodium in the water than before. The limit value for sodium in drinking water is 200 mg per liter (with the restriction that geogenically-related exceedances of up to 500 mg/l are permitted). Whether you exceed the limit depends on how much sodium you already have in your water. You can find out about this from your local waterworks.

Salt consumption is increasing

Basically, the higher the residual hardness, the lower the salt consumption. But: the higher the residual hardness, the more lime remains. We therefore set our systems to a residual hardness of 4 °dH as standard. This is a good compromise between saving salt and remaining lime in the water.

Conclusion

If your water hardness is below 20 °dH before softening, you usually don't have to worry about anything. A residual hardness of 0 °dH is possible. The only factor you should consider when adjusting the residual hardness is the sodium content. If the water hardness is over 20 °dH, the water is not automatically undrinkable, but we must point out that you are probably exceeding the limit. Our softening system is factory-set to a residual hardness of 4 °dH because this saves some salt and still causes very little limescale to form.