Water hardness and tap water in Castrop-Rauxel
Kreis Recklinghausen, Nordrhein-Westfalen · Postcode 44575, 44577, 44579, 44581
This page is a translation of the German version; the German page is authoritative. German version · Report a translation error
- Limits of the Drinking Water OrdinancemetAll tested parameters (17), at the waterworks
- Water hardness7.3 °dH, softNo legal limit, only a range
- Data coverageCore parameters: 7 of 7Score based on complete data
Verified drinking-water values
Note from the test report (in the German original): Gelsenwasser: „In Castrop-Rauxel erhalten Sie, wenn Sie in Becklem, Bladenhorst, Habinghorst, Henrichenburg, Ickern und Pöppinghausen wohnen, Trinkwasser aus dem Wasserwerk Haltern. Ebenso in Rauxel, nördlich Europaplatz/Grutholzallee sowie in Castrop in der Ahornstraße, Birkenstraße und Buchenstraße. Das übrige Stadtgebiet erhält Wasser aus dem Wasserwerk Witten. Bitte wählen Sie Ihr Wasserwerk aus.“ Hier die Jahresmittel 2025 des Wasserwerks Witten (übriges Stadtgebiet). Zum Vergleich Wasserwerk Haltern: 11,3 °dH (mittel), Nitrat 11,6 mg/l. Mikrobiologische Befunde weist Gelsenwasser für 2025 nicht als Mittelwert aus.
Background on household plumbing, not a measurement: in Castrop-Rauxel, 66 % of buildings with living space were built before 1970, and a further 8 % between 1970 and 1979 (Zensus 2022, Statistisches Bundesamt, dl-de/by-2-0). (Zensus 2022) According to the German Environment Agency (Umweltbundesamt), lead pipes exist at most in houses built before 1973 – and by no means in all of them. Whether there are any in your house is known to the owner or a plumber. (UBA)
What the values mean for Castrop-Rauxel
- Nitrate 10.7 mg/L – about 21 % of the limit of 50 mg/L and in the medium range – such values occur in catchments shaped by agriculture. Boiling does not reduce nitrate.
- PFAS (sum of PFAS-20) 28.3 ng/L – about 28 % of the limit of 100 ng/L (since 12 January 2026).
- Lead – not detectable at the waterworks. Lead gets into the water almost only through old lead pipes in household plumbing, not via the supplier.
- Uranium – not detectable at the waterworks (limit 10 µg/L).
- pH 7.92 – within the range of the Drinking Water Ordinance (6.5 to 9.5). The pH determines how corrosive the water is in household plumbing.
Water hardness in Castrop-Rauxel in everyday life
At 7.3 °dH, Castrop-Rauxel is in the hardness range “soft” (soft: below 8.4 °dH, medium: 8.4–14 °dH, hard: above 14 °dH).
- Dose detergent for the hardness range “soft” – the lowest amount on the pack.
- Limescale deposits are rare; kettles and coffee machines only need descaling every few months.
- At this hardness you do not need limescale protection or a water softener.
Baby food and low sodium: tap water in Castrop-Rauxel next to the bottled-water thresholds
Bottled water may only be labelled “suitable for preparing infant food” („geeignet für die Zubereitung von Säuglingsnahrung“) if it keeps to the maximum levels of the German Mineral and Table Water Ordinance (Mineral- und Tafelwasser-Verordnung, Annex 6). Here the published values for Castrop-Rauxel are shown next to them, each substance on its own. This is a comparison with labelling thresholds for bottled water, not a statement on whether your tap water is suitable for baby food. (Min/TafelWV, Anlage 6)
| Substance | Maximum level | Value in Castrop-Rauxel |
|---|---|---|
| Sodium | 20 mg/l | 24 mg/l – above |
| Nitrate | 10 mg/l | 10.7 mg/l – above |
| Nitrite | 0.02 mg/l | 0.01 mg/l – not above |
| Sulphate | 240 mg/l | 35 mg/l – not above |
| Fluoride | 0.7 mg/l | 0.09 mg/l – not above |
| Manganese | 0.05 mg/l | below the detection limit (0.002 mg/l) – not above |
| Arsenic | 0.005 mg/l | below the detection limit (0.0005 mg/l) – not above |
| Uranium | 0.002 mg/l | below the detection limit (0.001 mg/l) – not above |
For context: the German Environment Agency (Umweltbundesamt) considers preparing baby food with bottled water carrying this label necessary only in rare cases, for example when tap water is temporarily allowed to contain more than 50 mg/l nitrate. (UBA 2016, p. 59) Water from lead pipes in the house is always unsuitable for infants. (UBA 2020, p. 16) The values apply at the waterworks. Questions about baby food are answered by your midwife, your paediatrician and the health office (Gesundheitsamt).
Frequently asked questions about tap water in Castrop-Rauxel
Can you drink the tap water in Castrop-Rauxel?
According to the verified values, yes: All tested parameters with a legal limit (17) meet the limits set by the German Drinking Water Ordinance (TrinkwV). WaterScore: 100 out of 100 (data coverage: 7 of 7 core parameters). This applies to the water from the waterworks – restrictions can only arise from old household plumbing.
How hard is the water in Castrop-Rauxel?
The total hardness is 7.3 °dH – hardness range “soft”. Dose detergent for the hardness range “soft” – the lowest amount on the pack.
Is there PFAS in the tap water in Castrop-Rauxel?
Yes, in measurable amounts: according to the published analysis by Gelsenwasser (as of 2025), the sum of PFAS-20 is 0.0283 (middle of the range given by the supplier) µg/l – that is 28 % of the limit of 0.1 µg/l, which has applied since 12 January 2026.
Do I need to filter my tap water in Castrop-Rauxel?
Based on the verified supplier values, a filter is not necessary. It can make sense if you do not like the taste. If you suspect lead pipes in an old building, a filter does not help; a laboratory analysis at the tap does – that is a question of the household plumbing, not of the water leaving the works.
WaterScore
- Total100 / 100
- Chemical safety100 / 100
- Heavy metals100 / 100
- PFAS100 / 100
- Nutrients100 / 100
- General parameters100 / 100
- Data timeliness100 / 100
- Data quality100 / 100
Data coverage: 7 of 7 core parameters. Missing parameters are neither estimated nor counted as harmless: the score is based only on the values available. It is not a health assessment and says nothing about the water beyond the service connection. Methodology v3: how we calculate the WaterScore.
Evidence: cite and check
- Trinkwasseranalyse Castrop-Rauxel – Wasserwerk Witten, Jahresmittel 2025 (GELSENWASSER AG (Trinkwasseranalyse auf gelsenwasser.de)) · SHA-256 of the evaluated file: bf26fe07c50aa677…, checked on 3 October 2026
Suggested citation: Trinkwassermonitor (2025): Tap water in Castrop-Rauxel. Values according to the water supplier’s test report, sampling date 2025; at the waterworks, not household plumbing. https://trinkwassermonitor.ink/en/tap-water/castrop-rauxel/
JSON: /api/v1/evidence?city=castrop-rauxel
Data as of: 2025 · verified: 25 of 25 evaluated parameters.
This page shows only verified test data with sources, or states explicitly where data is missing (no estimated values). Cite as: “Trinkwassermonitor (2026). Tap water in Castrop-Rauxel. Retrieved from https://trinkwassermonitor.ink/en/tap-water/castrop-rauxel/.”