The degree of hardness of ...

The degree of hardness of drinking-water is important for aesthetic acceptability by consumers and for economic and operational considerations. Many hard waters are softened for those reasons using several applicable technologies, and the mineral composition will be significantly affected. The choice for the most appropriate conditioning technology will depend on local circumstances (e.g. water quality issues, piping materials, corrosion). Some softening is provided at the central treatment plant. Modification of calcium and magnesium concentrations in drinking-water for health reasons should comply with the technical requirements to provide water suitable for distribution and should not compromise disinfection. Softening is often carried out by means of ion exchangers.

These are ion exchangers that usually contain Na+ ions, which are released and substituted by Ca2+ and Mg2+ ions