Water hardness in Yerres
27.1 °fH very hard
Tap water in Yerres is very hard: 27.1 °fH (271 mg/L · 15.8 gpg · 15.2 °dH).
Source: Ministère de la Santé (ARS), contrôle sanitaire SISE-Eaux, commune 91691 (2026-08) · data checked 2026-10-19
In Yerres (Essonne), water supplied by Eau du Sud Parisien measures 271 mg/L as CaCO₃ and is classed as very hard. The value is measured, from the ARS health control (SISE-Eaux), August 2026 reading. It is a guide for the commune, not for a specific address.
TH en °fH : douce < 15, moyennement dure 15–25, dure 25–35, très dure > 35 °fH (classes usuelles ARS).
Water data
| Total hardness | 27.1 °fH |
|---|---|
| Utility | Eau Du Sud Parisien |
How Yerres compares
- Tap water in Yerres is 13 % harder than the median of the 33641 cities we track in France (23.9 °fH).
- By hardness it ranks 12713 of 33641 in France (1 = hardest); 62 % of these cities have softer water.
- In Essonne it is number 72 of 194 cities; the regional median is 25.9 °fH.
- Nearest city with clearly softer water: Villebon-sur-Yvette, 18 km away (19 °fH).
- Nearest city with clearly harder water: Le Blanc-Mesnil, 25 km away (36.7 °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 Yerres
| 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 Yerres water hard or soft?
It is very hard: 271 mg/L as CaCO₃ (15.8 gpg, 15.2 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Yerres 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 Yerres water?
15.8 gpg, equal to 15.2 °dH, 27.1 °fH or 271 mg/L calcium carbonate.
What dishwasher salt setting should I use in Yerres?
For 271 mg/L (15.2 °dH) check your manufacturer's table: maximum level (5–7).
Do I need a water softener in Yerres?
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 91691 (2026-08). Method: own measurement. Ministère de la Santé (ARS), contrôle sanitaire SISE-Eaux, commune 91691 · Outdated figure? Tell us