Water hardness and tap water in Marl

Kreis Recklinghausen, Nordrhein-Westfalen · Postcode 45768, 45770, 45772

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 hardness11.3 °dH, mediumNo 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): Jahresmittelwerte 2025 (2 bis 421 Einzelproben je Parameter, kein einzelnes Probenahmedatum). Marl wird komplett aus dem Wasserwerk Haltern der GELSENWASSER AG versorgt (ein Wertesatz für die ganze Stadt). Das Dokument wird von den Stadtwerken Lünen gehostet, die ebenfalls aus dem Wasserwerk Haltern beliefert werden – es ist GELSENWASSER AGs eigene, echte Analyse, keine Schätzung eines Dritten. Die Analyse enthält keine PFAS-Werte; diese stammen aus der Online-Trinkwasseranalyse von Gelsenwasser (Jahres-Mittel 2025, eigene Quelle). PFAS-Werte des Wasserwerks Haltern aus der Online-Trinkwasseranalyse von Gelsenwasser: Jahres-Mittel 2025 aus 4 Proben. Summe PFAS-4: 0,0075 µg/l (Grenzwert ab 12.01.2028: 0,020 µg/l).

Is a value wrong or out of date? Report an error – we check every report against the original source.

Background on household plumbing, not a measurement: in Marl, 60 % 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 Marl

• Nitrate 11.6 mg/L – about 23 % 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) 18.3 ng/L – about 18 % 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 1 µg/L – unremarkable against a limit of 10 µg/L. In some regions uranium occurs naturally from the rock (geogenic).
• pH 7.55 – 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 Marl in everyday life

At 11.3 °dH, Marl is in the hardness range “medium” (soft: below 8.4 °dH, medium: 8.4–14 °dH, hard: above 14 °dH).

• Dose detergent for the hardness range “medium”.
• As a rule of thumb, descale the kettle about every four to six weeks and the coffee machine as the manufacturer recommends.
• A limescale protection device is not a must at medium hardness; regular descaling is often enough.

Baby food and low sodium: tap water in Marl 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 Marl 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)

Against the other thresholds of Annex 6, the water would qualify as: low in sodium (“suitable for a low-sodium diet”) (Sodium 19 mg/l, threshold below 20 mg/l).

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 Marl

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

• Analyse 2025 für das Trinkwasser aus dem Wasserwerk Haltern (veröffentlicht von den Stadtwerken Lünen) (GELSENWASSER AG) · SHA-256 of the evaluated file: 350ea30b4792c488…, checked on 3 October 2026
• Trinkwasseranalyse Gelsenwasser – Wasserwerk Haltern, PFAS (Jahres-Mittel 2025) (GELSENWASSER AG (Trinkwasseranalyse auf gelsenwasser.de))

Suggested citation: Trinkwassermonitor (2025): Tap water in Marl. Values according to the water supplier’s test report, sampling date 2025; at the waterworks, not household plumbing. https://trinkwassermonitor.ink/en/tap-water/marl/

JSON: /api/v1/evidence?city=marl

Data as of: 2025 · verified: 26 of 26 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 Marl. Retrieved from https://trinkwassermonitor.ink/en/tap-water/marl/.”

Further information

• German version: Trinkwasser in Marl
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