Für den Gebrauch als Kesselspeisewasser (und da fallen je nach Größe der Anlage ähnliche Mengen an) wird Ionenaustausch verwendet. Siehe Zitat
The simplest form of demineralization of groundwater (e.g., for boiler feed water) consists of the subsequent application of a strongly acidic resin in the H+ form and a strongly or weakly basic resin in the OH– form or free-base form, respectively. Depending on the composition and quality of the fresh water to be treated and the desired product water quality, a weakly acidic resin can also be applied in the first step followed by a strongly or weakly basic anion-exchange resins [176]. This process design also saves regeneration costs. The development of the state of the water can be compiled easily from the previous sections.
[176] K. Dorfner : Ion Exchangers, De Gruyter, Berlin 1991, chap. 2.2.
Wenns nicht ganz so salzfrei sein soll, ist Umkehrosmose vielleicht anwendbar.
Gandalf