Water hardness in Fos-sur-Mer
34.2 °fH very hard
Tap water in Fos-sur-Mer is very hard: 34.2 °fH (342 mg/L · 20 gpg · 19.2 °dH).
Source: Ministère de la Santé (ARS), contrôle sanitaire SISE-Eaux, commune 13039 (2026-08) · data checked 2026-10-19
Range across supply zones: 339–344 mg/L.
Fos-sur-Mer in Bouches-du-Rhône is served by Suez and the Marseille port authority. The area depends largely on the Durance and Verdon (according to the Métropole), limestone-rich Alpine rivers: 342 mg/L CaCO₃, ranging from 339 to 344 mg/L. The water is very hard.
TH en °fH : douce < 15, moyennement dure 15–25, dure 25–35, très dure > 35 °fH (classes usuelles ARS).
Water data
| Total hardness | 34.2 °fH |
|---|---|
| Utility | Gd Port Maritime De Marseille Ouest; Suez Eau France |
How Fos-sur-Mer compares
- Tap water in Fos-sur-Mer is 43 % harder than the median of the 33641 cities we track in France (23.9 °fH).
- By hardness it ranks 3401 of 33641 in France (1 = hardest); 89 % of these cities have softer water.
- In Bouches-du-Rhône it is number 23 of 118 cities; the regional median is 22.4 °fH.
- Nearest city with clearly softer water: Saint-Mitre-les-Remparts, 6 km away (22.4 °fH).
- Nearest city with clearly harder water: Auriol, 56 km away (43.2 °fH).
Ranking of the hardest and softest water in France →
What it means at home
- Severe scale: heater elements and washing-machine heaters fail early.
- Detergent use is very high; taps and screens coat within days.
- Dishwasher at maximum salt setting.
- An ion-exchange softener is practically essential; RO for drinking water.
How much salt will you use for softening?
Yes. At this hardness a softener pays for itself through appliance life and detergent.
Descale a coffee machine or kettle about every 1 months (typical manufacturer guidance for this hardness).
Estimates for planning, not a quote. Check your appliance manual for exact settings.
Dishwasher setting in Fos-sur-Mer
| Brand | Setting for this water |
|---|---|
| Bosch | H05 |
| Miele | 19 °dH |
| AEG / Electrolux | 5 |
| Beko | 5th |
| Hoover | S3 |
| LG | H3 |
From each brand's manual for the model family named in the source; your model may differ, so check its manual. All brands and how to change the setting →
FAQ
Is Fos-sur-Mer water hard or soft?
It is very hard: 342 mg/L as CaCO₃ (20 gpg, 19.2 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Fos-sur-Mer safe to drink?
Hardness is not a health issue; it is about limescale, taste and appliances. Mains water must meet national drinking-water standards. TH en °fH : douce < 15, moyennement dure 15–25, dure 25–35, très dure > 35 °fH (classes usuelles ARS).
How many grains per gallon is Fos-sur-Mer water?
20 gpg, equal to 19.2 °dH, 34.2 °fH or 342 mg/L calcium carbonate.
What dishwasher salt setting should I use in Fos-sur-Mer?
For 342 mg/L (19.2 °dH) check your manufacturer's table: maximum level (5–7).
Do I need a water softener in Fos-sur-Mer?
Yes, unless you are only passing through: scale damages appliances within a few years.
Source
Source: Ministère de la Santé (ARS), contrôle sanitaire SISE-Eaux, commune 13039 (2026-08). Method: own measurement. Ministère de la Santé (ARS), contrôle sanitaire SISE-Eaux, commune 13039 · Outdated figure? Tell us