Hardness affects the amount of soap that is needed to produce foam or lather. Hard water requires more soap, because the calcium and magnesium ions form complexes with soap, preventing the soap from sudsing.
Hard water can also leave a film on hair, fabrics, and glassware.
Hardness of the water is very important in industrial uses, because it forms scale in heat exchange equipment, boilers, and pipe lines. Some hardness is needed in plumbing systems to prevent corrosion of pipes. The greater the hardness, the harder it is for toxic metals to be absorbed through the gills. Measurement of Hardness Hardness is generally measured by titration. A buffer and a color indicator are added to a volume of water.