DGH

Degrees of general hardness (dGH) is a unit of water hardness, specifically of general hardness. General hardness is a measure of the concentration of divalent metal ions such as calcium and magnesium (Ca²⁺, Mg²⁺) per volume of water. Specifically, 1 dGH is defined as 10 milligrams (mg) of calcium oxide (CaO) per litre of water, which is equivalent to 0.17832 mmol per litre of elemental calcium and/or magnesium ions, since CaO has a molar mass of 56.0778 g/mol.

In water testing, paper strips often measure hardness in parts per million (ppm), where one part per million is defined as one milligram of calcium carbonate (CaCO₃) per litre of water. Consequently, 1 dGH corresponds to 17.848 ppm, since CaCO₃ has a molar mass of 100.0875 g/mol.

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