text: Dissolved ions may affect the suitability of water for a range of industrial and domestic purposes. The most familiar of these is probably the presence of calcium (Ca) and magnesium (Mg) that interfere with the cleaning action of soap, and can form hard sulfate and soft carbonate deposits in water heaters or boilers. Hard water may be softened to remove these ions. The softening process often substitutes sodium cations. For certain populations, hard water may be preferable to soft water because health problems have been associated with calcium deficiencies and with excess sodium. The necessity for additional calcium and magnesium in water depends on the population in question because people generally satisfy their recommended amounts through food.