Water hardness in Osny
26.4 °fH very hard
Tap water in Osny is very hard: 26.4 °fH (264 mg/L · 15.4 gpg · 14.8 °dH).
Source: Ministère de la Santé (ARS), contrôle sanitaire SISE-Eaux, commune 95476 (2026-06) · data checked 2026-10-19
Range across supply zones: 260–269 mg/L.
Osny in Val-d'Oise is served by Cyo' and SFDE. The Cergy-Pontoise area lies in the Oise valley on Paris Basin limestone: 264 mg/L CaCO₃, ranging from 260 to 269 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 | 26.4 °fH |
|---|---|
| Utility | Cyo'; Sfde - Agence De Cergy |
How Osny compares
- Tap water in Osny is 10 % harder than the median of the 33641 cities we track in France (23.9 °fH).
- By hardness it ranks 13658 of 33641 in France (1 = hardest); 59 % of these cities have softer water.
- In Val-d'Oise it is number 114 of 149 cities; the regional median is 30.6 °fH.
- Nearest city with clearly softer water: Saint-Ouen-l'Aumône, 4 km away (19.5 °fH).
- Nearest city with clearly harder water: Ennery, 4 km away (41.7 °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 Osny
| Brand | Setting for this water |
|---|---|
| Bosch | H04 |
| Miele | 15 °dH |
| AEG / Electrolux | 4 |
| Beko | 4th |
| Hoover | S2 |
| 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 Osny water hard or soft?
It is very hard: 264 mg/L as CaCO₃ (15.4 gpg, 14.8 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Osny 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 Osny water?
15.4 gpg, equal to 14.8 °dH, 26.4 °fH or 264 mg/L calcium carbonate.
What dishwasher salt setting should I use in Osny?
For 264 mg/L (14.8 °dH) check your manufacturer's table: maximum level (5–7).
Do I need a water softener in Osny?
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 95476 (2026-06). Method: own measurement. Ministère de la Santé (ARS), contrôle sanitaire SISE-Eaux, commune 95476 · Outdated figure? Tell us