Water hardness in Conflans-Sainte-Honorine
34.4 °fH very hard
Tap water in Conflans-Sainte-Honorine is very hard: 34.4 °fH (344 mg/L · 20.1 gpg · 19.3 °dH).
Source: Ministère de la Santé (ARS), contrôle sanitaire SISE-Eaux, commune 78172 (2026-08) · data checked 2026-10-19
In Conflans-Sainte-Honorine, at the confluence of the Seine and the Oise, drinking water is treated at a plant from these rivers. It reaches 344.0 mg/L CaCO₃, among the hardest water in the region. A softener is often considered.
TH en °fH : douce < 15, moyennement dure 15–25, dure 25–35, très dure > 35 °fH (classes usuelles ARS).
Water data
| Total hardness | 34.4 °fH |
|---|---|
| Utility | Societe Des Eaux De Fin D'Oise |
How Conflans-Sainte-Honorine compares
- Tap water in Conflans-Sainte-Honorine is 44 % harder than the median of the 33641 cities we track in France (23.9 °fH).
- By hardness it ranks 3293 of 33641 in France (1 = hardest); 90 % of these cities have softer water.
- In Yvelines it is number 13 of 222 cities; the regional median is 23 °fH.
- Nearest city with clearly softer water: Éragny, 2 km away (19.5 °fH).
- Nearest city with clearly harder water: Noisy-sur-Oise, 23 km away (43.4 °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 Conflans-Sainte-Honorine
| 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 Conflans-Sainte-Honorine water hard or soft?
It is very hard: 344 mg/L as CaCO₃ (20.1 gpg, 19.3 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Conflans-Sainte-Honorine 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 Conflans-Sainte-Honorine water?
20.1 gpg, equal to 19.3 °dH, 34.4 °fH or 344 mg/L calcium carbonate.
What dishwasher salt setting should I use in Conflans-Sainte-Honorine?
For 344 mg/L (19.3 °dH) check your manufacturer's table: maximum level (5–7).
Do I need a water softener in Conflans-Sainte-Honorine?
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 78172 (2026-08). Method: own measurement. Ministère de la Santé (ARS), contrôle sanitaire SISE-Eaux, commune 78172 · Outdated figure? Tell us