A method is provided for decalcification of an aqueous solution that has multivalent Ca2+ and Mg2+ cations and anions able to form complexes with at least a part of the multivalent cations. The method includes replacing at least part of the anions to form complexes of the aqueous solution by monovalent anions such as Cl−, non-able to form such complexes. The method also replaces at least a part of the multivalent cations of the aqueous solution by monovalent metal cations such as Na+ and/or K+. This later replacement step is performed simultaneously with or after the first replacement step.
