Water hardness in Cologne
16.9 °dH very hard
Tap water in Cologne is very hard: 16.9 °dH (301 mg/L · 17.6 gpg · 30.1 °fH).
Source: RheinEnergie, Trinkwasseranalyse Köln linksrheinisch und Pulheim, Jahresmittelwerte 2025 (Ausgabe 2026) (2025) · data checked 2026-10-22
Range across supply zones: 279–323 mg/L.
2 supply zones — hardness varies by neighbourhood; the figure above is the median.
Hardness by district / supply zone
| °dH | mg/L | ||
|---|---|---|---|
| Linksrheinisch (Wasserwerke Hochkirchen und Weiler) | 18.1 | 323 | very hard |
| Rechtsrheinisch (Wasserwerke Höhenhaus und Zündorf) | 15.6 | 279 | very hard |
RheinEnergie publishes 2025 annual mean analyses for Cologne, split into a left-bank and a right-bank network. The left bank (Hochkirchen and Weiler waterworks) reports 323.1 mg/L CaCO₃ and the right bank (Höhenhaus and Zündorf) 278.5 mg/L, so the city figure of 300.8 mg/L depends on which side of the Rhine you live. Calcium is listed at 88 mg/L and magnesium at 14 mg/L. Check the network for your street before sizing a softener.
German law (WRMG) uses 3 bands: soft < 8.4 °dH, medium 8.4–14 °dH, hard > 14 °dH.
Water data
| Total hardness | 16.9 °dH |
|---|---|
| Calcium (mg/L) | 88 |
| Magnesium (mg/L) | 14 |
| Utility | RheinEnergie AG |
How Cologne compares
- Tap water in Cologne is 47 % harder than the median of the 809 cities we track in Germany (11.5 °dH).
- By hardness it ranks 193 of 809 in Germany (1 = hardest); 76 % of these cities have softer water.
- In Nordrhein-Westfalen it is number 18 of 153 cities; the regional median is 11.3 °dH.
- Nearest city with clearly softer water: Hürth, 8 km away (10.1 °dH).
- Nearest city with clearly harder water: Limburg an der Lahn, 99 km away (23.3 °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 Cologne
| Brand | Setting for this water |
|---|---|
| Bosch | H05 |
| Miele | 17 °dH |
| AEG / Electrolux | 4 |
| 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 Cologne water hard or soft?
It is very hard: 301 mg/L as CaCO₃ (17.6 gpg, 16.9 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Cologne 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 Cologne water?
17.6 gpg, equal to 16.9 °dH, 30.1 °fH or 301 mg/L calcium carbonate.
What dishwasher salt setting should I use in Cologne?
For 301 mg/L (16.9 °dH) check your manufacturer's table: maximum level (5–7).
Do I need a water softener in Cologne?
Yes, unless you are only passing through: scale damages appliances within a few years.
Source
Source: RheinEnergie, Trinkwasseranalyse Köln linksrheinisch und Pulheim, Jahresmittelwerte 2025 (Ausgabe 2026) (2025). Method: figure published by the water supplier. RheinEnergie, Trinkwasseranalyse Köln linksrheinisch und Pulheim, Jahresmittelwerte 2025 (Ausgabe 2026) · Outdated figure? Tell us