Water composition

Water hardness and composition

The hardness represents the amount of calcium and magnesium dissolved in the water.

Water hardness is generally expressed in French degrees (°f or °fH).
It is sometimes expressed in German degrees (°dH).

 1 French degree (°f or °fH) is equal to

  • 4 mg/l of calcium
  • 2.43 mg/l of magnesium
  • 10 ppm or 10 mg/l of calcium carbonate
  • 0.1 millimole per litre of calcium carbonate (mmol/l)
  • 0.2 milliequivalent per litre of calcium carbonate (meq/l)
  • 0.56 German degree (°dH)

Lime scale = calcium carbonate (CaCO3)


Water hardness scale:

from 0 to 5°fH:  very soft water
from 5 to 15°fH: soft water
from 15 to 25°fH: medium hard water
from 25 to 40°fH: hard water
> to 40°fH:       very hard water