What is water hardness?
Water hardness measures the concentration of dissolved calcium ions (Ca²⁺) and magnesium ions (Mg²⁺). In France, it is expressed in French degrees (°f) — also called TH (titre hydrométrique). One French degree corresponds to 10 mg/L of calcium carbonate (CaCO₃).
Water is classified on the following scale:
| Hardness (°f) | Classification | Characteristic |
|---|---|---|
| 0 – 8°f | Very soft | Aggressive water, risk of pipe corrosion |
| 8 – 15°f | Soft | Little limescale, optimal comfort |
| 15 – 25°f | Moderately hard | Moderate limescale, first deposits possible |
| 25 – 35°f | Hard | Visible limescale, impact on appliances |
| > 35°f | Very hard | Rapid scaling, significant energy overconsumption |
Water hardness depends on the geology of the subsoil: regions with limestone bedrock (sedimentary basins) have hard water, while granitic or volcanic regions have soft water.
Map of France: the most affected regions
In France, approximately 80% of households are supplied with moderately hard to very hard water (above 15°f). Here is the breakdown by major region, based on data from Regional Health Agencies (ARS) and the qualite-eau.fr portal:
Hard to very hard water regions (> 25°f)
| Region | Typical hardness (°f) | Subsoil |
|---|---|---|
| Île-de-France | 25 – 40°f | Limestone Paris Basin |
| Hauts-de-France | 25 – 45°f | Chalk of the Artois basin |
| Grand Est | 25 – 40°f | Jurassic limestone, calcareous Vosges |
| Bourgogne-Franche-Comté | 25 – 45°f | Jurassic limestone plateaux |
| Centre-Val de Loire | 20 – 35°f | Beauce limestone |
| Normandy | 20 – 35°f | Pays de Caux chalk |
| Provence-Alpes-Côte d'Azur | 25 – 40°f | Provençal limestone |
| Occitanie (east) | 20 – 35°f | Causses limestone, garrigue |
Soft water regions (< 15°f)
| Region | Typical hardness (°f) | Subsoil |
|---|---|---|
| Brittany | 5 – 15°f | Armorican Massif (granite, schist) |
| Massif Central (Auvergne) | 3 – 12°f | Volcanic rocks |
| Vosges (western slope) | 5 – 12°f | Vosges sandstone and granite |
| Pyrenees | 5 – 15°f | Pyrenean granite and schist |
| Corsica | 5 – 15°f | Corsican granite |
| Landes / Basque Country | 8 – 18°f | Sand and siliceous rocks |
Water hardness by city: key figures
| City | Hardness (°f) | Classification |
|---|---|---|
| Paris | 25 – 30°f | Hard |
| Marseille | 28 – 33°f | Hard |
| Lyon | 20 – 30°f | Moderately hard to hard |
| Toulouse | 20 – 30°f | Moderately hard to hard |
| Nice | 25 – 32°f | Hard |
| Lille | 30 – 40°f | Hard to very hard |
| Strasbourg | 25 – 35°f | Hard |
| Bordeaux | 18 – 28°f | Moderately hard to hard |
| Nantes | 15 – 22°f | Moderately hard |
| Montpellier | 28 – 38°f | Hard to very hard |
| Rennes | 10 – 18°f | Soft to moderately hard |
| Clermont-Ferrand | 5 – 10°f | Very soft to soft |
| Dijon | 28 – 38°f | Hard to very hard |
| Reims | 30 – 40°f | Hard to very hard |
| Besançon | 30 – 42°f | Very hard |
Values vary by neighbourhood and supply source. For the exact hardness of your water, consult qualite-eau.fr or your local ARS.
How to check your water hardness
- qualite-eau.fr — Official portal of the French Ministry of Health. Enter your municipality and consult the latest ARS analysis. Hardness is indicated in °f under "Physico-chemical parameters".
- Your water bill — Most distributors (Veolia, Suez, Saur, municipal utilities) indicate the average TH on the annual bill or their website.
- UFC-Que Choisir — The interactive "Water Quality" map from UFC allows visualising hardness by municipality.
- Test strips — Available at pharmacies or aquarium shops, they provide a quick hardness estimate in seconds.
- LIMPEO calculator — Our savings calculator incorporates your water hardness to estimate potential gains.
The consequences of hard water on your home
- Pipes — Limescale reduces pipe diameter, decreases flow rate and can cause blockages. A 15 mm pipe can narrow to 8 mm within a few years at 35°f.
- Water heater and boiler — Every millimetre of limescale on an element increases energy consumption by 7% (source: ADEME). At 3 mm: +21% on the bill. Read also: Limescale costs you 25% on your energy bill.
- Household appliances — Washing machine, dishwasher, kettle, coffee machine: limescale reduces their lifespan by 30 to 50% and increases breakdowns.
- Skin and hair — Hard water dries the skin, causes irritation and leaves hair dull and brittle. People with eczema or dermatitis are particularly sensitive.
The solution: LIMPEO electromagnetic treatment
LIMPEO, by JAEGER SAS, transforms calcite into aragonite through electromagnetic waves, preventing limescale from depositing. Effective for all hardness levels, from 15°f to 45°f.
- 88% scale reduction — scientifically validated
- 10-minute installation, zero maintenance for 10 years
- Compatible with all pipe types
Discover our product range and calculate your savings with our online tools.
FAQ — Hard water map France
How do I know if my water is hard?
The most reliable method: consult qualite-eau.fr with your municipality name. You can also check your annual water bill (TH often indicated), or use test strips available at pharmacies.
What is the hardest water in France?
The hardest regions are Hauts-de-France (up to 45°f in some areas near Lille), Bourgogne-Franche-Comté (Jura plateaux), and Grand Est. Some cities like Besançon can reach 42°f.
Can limescale damage my health?
No. Calcium and magnesium are beneficial minerals. Hard water is not dangerous for health. The problems are technical: limescale damages appliances, increases energy consumption and causes skin dryness.