What is water hardness?
Water hardness measures dissolved calcium and magnesium, expressed in mg/L CaCO₃ or °dH (German degrees) or °f (French degrees).
Classification: Soft <100 mg/L · Moderately hard 100–200 mg/L · Hard 200–300 mg/L · Very hard >300 mg/L
Hardness by European and major city
| City | mg/L CaCO₃ | Classification |
| Barcelona 🇪🇸 | 320 | Extremely hard |
| London 🇬🇧 | 300 | Very hard |
| Rome 🇮🇹 | 300 | Very hard |
| Naples 🇮🇹 | 280 | Very hard |
| Berlin 🇩🇪 | 250 | Hard–Very hard |
| Brussels 🇧🇪 | 250 | Hard |
| Amsterdam 🇳🇱 | 210 | Hard |
| Paris 🇫🇷 | 190 | Hard (~30°f) |
| Dublin 🇮🇪 | 180 | Moderately hard |
| Hamburg 🇩🇪 | 160 | Moderately hard |
| Lisbon 🇵🇹 | 150 | Moderately hard |
| Madrid 🇪🇸 | 60 | Soft |
| New York 🇺🇸 | 20 | Very soft (high chloramine) |
Note: Even "soft" water cities like Madrid and New York treat water heavily with chlorine/chloramines — making a shower filter beneficial regardless of hardness.
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