Title: hard water
Long Title: IUPAC Gold Book - hard water
DOI: 10.1351/goldbook.14730
Status: current

Definition
Water that contains mineral salts of divalent cations, commonly calcium and magnesium and sometimes iron(II) (ferrous) ions, principally as hydrogencarbonates, chlorides, and sulfates.

Note
Hardness caused by calcium hydrogencarbonate is known as temporary, because boiling converts the hydrogencarbonate to calcium carbonate (\(\ce{CaCO3}\)), which has a very low solubility; hardness from the other salts is called permanent.

Source
- PAC, 2009, 81, 829. 'Glossary of terms used in ecotoxicology (IUPAC Recommendations 2009)' on page 893 (https://doi.org/10.1351/PAC-REC-08-07-09)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/14730/html
- json: https://goldbook.iupac.org/terms/view/14730/json
- xml: https://goldbook.iupac.org/terms/view/14730/xml

Citation: Citation: 'hard water' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.14730
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Accessed: 2026-06-29T08:42:50+00:00