Conversion Factors for Units in the Water Chemistry

Hardness, Total Alkaline Earths

The factors for conversion of units relating to different substances are approximate, assuming a distribution of hardness as common in natural waters.

Quantity Unit mmol/l mval/l °dH °eH °fH ppm CaCO3
total alkaline earths 1 mmol/l = 1 2 5.6 7.02 10 100
total alkaline earths 1 mval/l = 0.5 1 2.8 3.51 5 50
German hardness 1 °dH = 10 mg/l CaO = 0.1783 0.357 1 1.253 1.78 17.8
English hardness 1 °eH = 1 grain/gallon CaCO3 = 0.142 0.285 0.798 1 1.43 14.3
French hardness 1 °fH = 10 g/m³ CaCO3 = 0.1 0.2 0.560 0.702 1 10
hardness as CaCO3 1 ppm CaCO3 = 1 mg/kg CaCO3 = 0.01 0.02 0.056 0.07 0.1 1

General Units of Concentration

The units ppm (parts per million) = mg/kg and ppb (parts per billion) = μg/kg can be converted to mg/l and μg/l using the factor 1 (approximate, exact at a water temperature of 4 °C).

Unit mmol/l mval/l mg/l ppm CaCO3
1 mmol/l = 1 [valency] [molar mass] 100.09
1 mval/l = 1 / [valency] 1 [molar mass] / [valency] 100.09 / [valency]
1 mg/l = 1 / [molar mass] [valency] / [molar mass] 1 100.09 / [molar mass]
1 ppm CaCO3 = 1 / 100.09 [valency] / 100.09 [molar mass] / 100.09 1

Conductivity and Salt Content (TDS)

The factors for conversion between conductivity and salt content are approximate, assuming a water temperature of 20 °C and a conductivity of ≥ 1 μS/cm and ≤ 1000 μS/cm.

Quantity Unit μS/cm MΩ cm mmol/l NaCl mg/l NaCl
conductivity σ 1 μS/cm = 1 1 / σ² 0.009 0.53
resistivity ρ 1 MΩ cm = 1 / ρ² 1 111 1.89
salt content 1 mmol/l NaCl = 111 0.009 1 58.44
salt content 1 mg/l NaCl = 1.89 0.53 0.0171 1

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