Water softening generally involves the replacement of calcium and magnesium ions by sodium ions. The water becomes softer and foams and when it is heated in electrode humidifiers there is a considerable increase in water conductivity, because the hardeners now hardly deposit limescale.
Water demineralisation removes all mineral salts from the water. There are essentially two different systems. The ion exchanger and reverse osmosis. Ion exchangers are one method for the complete demineralisation of feed water. Special resins replace all the cations contained in the raw water for hydrogen ions (H) and all the associated anions for hydroxyl ions. The hydroxyl groups and hydrogen ions combine to form H2O (water). Depending on the output requirement, ion exchangers operate with a 2-column system in which the ion exchangers are separately incorporated (one in each column). For small to medium outputs, a mixed-bed is used, in which both resins are mixed in a container (cartridge).
Reverse osmosis: In reverse osmosis, after prior water softening, a semi-permeable membrane is used to remove all the mineral salts under pressure. Fully demineralised water has no inherent conductivity, therefore it is not suitable for use with an electrode steam humidifier and contains no hardeners. Therefore making it ideally suited as feed water for heater element steam humidifiers, which when operated with demineralised water are effectively maintenance-free, as there are no longer any hardeners to deposit out. Fully demineralised water can however still be very effectively diluted with tap water to form a less conductive feed water for electrode steam humidifiers, so that the cylinder operating times are considerably extended.