Water hardness in Mainz
19.3 °dH very hard
Tap water in Mainz is very hard: 19.3 °dH (345 mg/L · 20.1 gpg · 34.5 °fH).
Source: Mainzer Netze GmbH - Analysenwerte Trinkwasser Mittelwerte 2025 (2025) · data checked 2026-10-19
Range across supply zones: 225–448 mg/L.
3 supply zones — hardness varies by neighbourhood; the figure above is the median.
Hardness by district / supply zone
| °dH | mg/L | ||
|---|---|---|---|
| Wasserwerk Eich | 19.3 | 345 | very hard |
| Wasserwerk Hof Schoenau | 25.1 | 448 | very hard |
| Wasserwerk Petersaue | 12.6 | 225 | very hard |
Mainzer Netze publishes 2025 mean values for three waterworks: Hof Schönau, Petersaue and Eich. The median is 344.5 mg/L CaCO₃ and the range is 224.9 to 448.0 mg/L, so Hof Schönau water is about twice as hard as Petersaue water. Which works serves your address matters more than the city figure. The sheet does not map streets to works, so ask the utility.
German law (WRMG) uses 3 bands: soft < 8.4 °dH, medium 8.4–14 °dH, hard > 14 °dH.
Water data
| Total hardness | 19.3 °dH |
|---|
How Mainz compares
- Tap water in Mainz is 68 % harder than the median of the 809 cities we track in Germany (11.5 °dH).
- By hardness it ranks 89 of 809 in Germany (1 = hardest); 89 % of these cities have softer water.
- In Rheinland-Pfalz it is number 2 of 25 cities; the regional median is 9.9 °dH.
- Nearest city with clearly softer water: Taunusstein, 19 km away (10.3 °dH).
- Nearest city with clearly harder water: Nußloch, 83 km away (31.6 °dH).
Ranking of the hardest and softest water in Germany →
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 Mainz
| 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 Mainz water hard or soft?
It is very hard: 345 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 Mainz safe to drink?
Hardness is not a health issue; it is about limescale, taste and appliances. Mains water must meet national drinking-water standards. German law (WRMG) uses 3 bands: soft < 8.4 °dH, medium 8.4–14 °dH, hard > 14 °dH.
How many grains per gallon is Mainz water?
20.1 gpg, equal to 19.3 °dH, 34.5 °fH or 345 mg/L calcium carbonate.
What dishwasher salt setting should I use in Mainz?
For 345 mg/L (19.3 °dH) check your manufacturer's table: maximum level (5–7).
Do I need a water softener in Mainz?
Yes, unless you are only passing through: scale damages appliances within a few years.
Source
Source: Mainzer Netze GmbH - Analysenwerte Trinkwasser Mittelwerte 2025 (2025). Method: figure published by the water supplier. Mainzer Netze GmbH - Analysenwerte Trinkwasser Mittelwerte 2025 · Outdated figure? Tell us