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Measure of the amount of calcium and magnesium ions in water


  1. Calcium and magnesium compounds can precipate out of water to form deposits in sinks, pipes, etc. This can be of importance for boilers, water supply systems, and home pipes.
  2. Calcium and magnesium ions bind with soap and detergent reducing their effectiveness.


  • Typical values - ∼0 to >500 mg/L
  • There is no international standard on hardness. Hard water is general considered to be over ∼100 mg/L (different organizations used slightly different definitions).


Wilkes University Center for Environmental Quality