What value should the residual hardness be set to?

Table of Contents

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

Several theories exist regarding the setting of residual hardness. It is often claimed that soft water is dangerous for pipes and that the residual hardness should not be set below 8 °dH. With this article, we would like to shed some light on the matter.

Soft water is corrosive.

It is often claimed that soft water is corrosive. This claim is absolutely correct, but what is often overlooked 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, by definition, always contains oxygen (H₂O), it can corrode when in contact with metal. The problem of corrosion affects, for example, copper and galvanized steel pipes (rust or verdigris can form). This risk does not exist with plastic pipes. If you are experiencing problems with pipe corrosion (for example, a burst pipe), you should consider installing a dosing system , regardless of whether you are installing a water softener.

Does water softening change the pH value?

Our water softeners use the neutral exchange process. In this process, calcium and magnesium ions are exchanged for sodium ions. This does not change the pH value! Of course, there are other methods, such as reverse osmosis. With reverse osmosis, the pH value decreases, and the water becomes slightly acidic. However, we do not use this method in private households. Therefore, there is no reason to avoid low water hardness in your home.

The sodium content increases

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

Salt consumption is increasing

As a general rule: the higher the residual hardness, the lower the salt consumption. However, the higher the residual hardness, the more limescale remains. Therefore, we set our systems to a standard residual hardness of 4 °dH. This is a good compromise between salt savings and the amount of residual limescale in the water.

Conclusion

If your water hardness before softening is below 20 °dH, you generally don't need to do anything. A residual hardness of 0 °dH is possible. The only factor you should consider when setting the residual hardness is the sodium content. While water with a hardness above 20 °dH isn't automatically undrinkable, we must point out that you will likely exceed the limit. Our water softeners are factory-set to a residual hardness of 4 °dH because this saves on salt while still minimizing limescale buildup.