Water hardness in Luxembourg

Water hardness corresponds to the concentration of calcium (Ca²⁺) and magnesium (Mg²⁺) ions. The more calcareous rock the water has passed through before reaching the tap, the harder it is. In Luxembourg, the predominantly calcareous subsoil (particularly in the Gutland) produces water that is often moderately hard to hard, whereas the Oesling regions in the north yield softer water.

Luxembourg mainly uses the French degree (°fH). 1°fH = 10 mg/L of calcium carbonate. The official scale distinguishes: very soft (0–7°fH), soft (7–15°fH), moderately hard (15–25°fH), hard (25–35°fH) and very hard (>35°fH). In Germany and the Grand Duchy, the German degree (°dH) is also used: 1°dH = 1.79°fH.

Above 20°fH, limescale builds up in pipes, reduces flow, insulates water-heater elements (up to 30% additional consumption for 5 mm of scale), stains taps, stiffens laundry and dries out the skin. Over the long term, the lifespan of household appliances also drops. A water softener removes these ions in favour of sodium, neutralising the problem at the source.

Across 106 distribution zones analysed, more than 75% deliver water classified as soft to moderately hard. The municipalities most exposed to limescale are concentrated in the south and east of the country. Our interactive map lets you find out exactly how hard the water is in your municipality.