Hard water vs soft water — what's the difference?

Water hardness is expressed in French degrees (°fH) or mg/L of calcium carbonate. Hard water (>15 °fH) contains more calcium and magnesium. The WHO finds no convincing evidence that hard drinking water is harmful — it modestly contributes to daily mineral intake.

Much of Belgium, the Netherlands, the UK and southern Germany have fairly hard water (15–30 °fH). This causes limescale on kettles and faucets, but no health risk. A water softener is mainly a comfort and appliance-protection choice, not a health one.

Utilities publish local hardness maps; check your water company's website.

Source: WHO Hardness in Drinking-Water (2011, 2022 review).