Causes PBNO3 water hardness

To which value should the residual hardness be set?

There are some theories about the setting of the residual hardness. It is often said that soft water is dangerous for the pipelines and that the residual hardness should not be set lower than 8 ° dH. With this article we would like to shed some light on the darkness.

Soft water is corrosive

It is often said that soft water is corrosive. This claim is absolutely correct, but what is not mentioned is: Water is always corrosive, regardless of whether it is soft or hard. Corrosion is when a substance (often metal) reacts with oxygen. Since water, by definition, always contains oxygen (H2O), it can corrode in contact with metal. The problem with corrosion concerns, for example, copper and galvanized steel pipes (rust or verdigris can develop). This danger does not exist with plastic pipes. If you have problems with corrosion of pipes (for example a broken pipe) you should think about installing a dosing system regardless of the installation of a water softener.

Does the softening change the pH value?

Our water 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 methods such as reverse osmosis technology. With reverse osmosis softening, 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 a low water hardness here either.

The sodium content increases

Sodium, for example, is a component of table salt (NaCl) and a natural component in water. As already mentioned before, the neutral exchange (or also: ion exchange) increases the sodium content 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 of sodium more 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 the water. You can find out about this from your local water company.

The salt consumption increases

Basically, the higher the residual hardness, the lower the salt consumption. But: the higher the residual hardness, the more lime that remains. That is why we 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.


If your water hardness is below 20 ° dH before softening, you usually do not have to pay attention to anything. A residual hardness of 0 ° dH is possible. The only factor to consider when setting the residual hardness is the sodium content. If the water hardness is over 20 ° dH, the water is not automatically inedible, but we must point out that you will then probably exceed the limit value. Our water softener is factory-set to a residual hardness of 4 ° dH because this saves a little salt and very little lime is formed.