Hardness of water
Corrosion and sedimentation are the biggest risks for the durability of steam boilers.
Furthermore they can decrease effectiveness of the steam boiler and lead to higher energy consumption and interference liability.
Hence a steam boiler should only be run with soft water low at calcium carbonate and salt.
Best is water at 1-4° German hardness (Hint: one degree German hardness is equivalent to 10mg calcium carbonate (CaO) per kg water).
Rain water which is properly stored is most suitable.
Less soft ground or tap water should be treated to avoid corrosion or sedimentation of calcium carbonate in the inside of the boiler. Most manufacturers of steam boilers install a softening plant for normal hard water at their standard model.
For water with a high content of calcium carbonate and Für magnesium (starting from 14° German hardness) special plants for water treatments have to be used. These are e.g. ionic exchangers or reverse osmosis filter.