For heating installations with Aluminium/Silicon alloy heat exchangers (50 - 600kW), the water in the heating system must be deionised / demineralised / desalinated (this is the same thing!).

The electrical conductivity must not exceed 10 microS/cm. Chemically pure water suitable for heat transfer is not available in the mains water supply, you have to control the water quality. The properties of the water and therefore the quality of the water are determined by the minerals in the water. If the water quality is low, the heating system can be damaged by scale and corrosion.