Limescale in water treatment

Central softening

High hardness (calcium and magnesium ions) of drinking water has disadvantages for household use. Around 8 °dH (degree of German hardness) or around 1.43 mmol/L is considered a favorable range. If the hardness of the water is much higher (e.g. over 20 °dH), softening may be advisable. However, the hardness must not be too low; if it is below 3 °dH, it must be hardened in any case. Softening can be carried out centrally at the waterworks or decentrally as post- treatment in the household. However, only part of the hardness components are removed (partial softening), as residual hardness is required. During softening, the hardness constituents (calcium and magnesium ions) are removed from the water. This can be done using ion exchange processes and precipitation processes. Carbonic acid is only involved in precipitation processes in which the lime-carbonic acid equilibrium is exceeded by raising the pH value and lime (calcite) is precipitated.