Water hardness in Trappes
18 °fH very hard
Tap water in Trappes is very hard: 18 °fH (180 mg/L · 10.5 gpg · 10.1 °dH).
Source: Ministère de la Santé (ARS), contrôle sanitaire SISE-Eaux, commune 78621 (2026-08) · data checked 2026-10-19
Range across supply zones: 178–232 mg/L.
In Trappes (Yvelines), the reported value is 180 mg/L CaCO₃ (18 °f), within a range of 178 to 232 mg/L. That is very hard water. Two suppliers appear in the data: S.E.O.P. and Veolia Eau. Source: ARS sanitary monitoring, August 2026.
TH en °fH : douce < 15, moyennement dure 15–25, dure 25–35, très dure > 35 °fH (classes usuelles ARS).
Water data
| Total hardness | 18 °fH |
|---|---|
| Utility | S.E.O.P.; Veolia Eau - Cge |
How Trappes compares
- Tap water in Trappes is 25 % softer than the median of the 33641 cities we track in France (23.9 °fH).
- By hardness it ranks 21756 of 33641 in France (1 = hardest); 35 % of these cities have softer water.
- In Yvelines it is number 185 of 222 cities; the regional median is 23 °fH.
- Nearest city with clearly softer water: Saint-Léger-en-Yvelines, 18 km away (11.4 °fH).
- Nearest city with clearly harder water: Le Mesnil-Saint-Denis, 5 km away (23 °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 Trappes
| Brand | Setting for this water |
|---|---|
| Bosch | H02 |
| Miele | 10 °dH |
| AEG / Electrolux | 2 |
| Beko | 3rd |
| Hoover | S2 |
| LG | H2 |
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 Trappes water hard or soft?
It is very hard: 180 mg/L as CaCO₃ (10.5 gpg, 10.1 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Trappes 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 Trappes water?
10.5 gpg, equal to 10.1 °dH, 18 °fH or 180 mg/L calcium carbonate.
What dishwasher salt setting should I use in Trappes?
For 180 mg/L (10.1 °dH) check your manufacturer's table: maximum level (5–7).
Do I need a water softener in Trappes?
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 78621 (2026-08). Method: own measurement. Ministère de la Santé (ARS), contrôle sanitaire SISE-Eaux, commune 78621 · Outdated figure? Tell us