London
London, United Kingdom has an estimated water hardness of 272 ppm (mg/L as calcium carbonate), which is classed as very hard. High scale risk. Configure appliances and descale regularly.
London water hardness in every unit
| Unit | Average |
|---|---|
| mg/L or ppm (CaCO₃) | 272 |
| mmol/L | 2.72 |
| German degrees (°dH) | 15.24 |
| French degrees (°fH) | 27.2 |
| Clark degrees (°e) | 19.08 |
| Grains per US gallon (gpg) | 15.89 |
Published range: 247–302 ppm.
Where London's water comes from
- Supplier: Four companies: Thames Water (about 76% of Londoners), Affinity Water, Essex & Suffolk Water and SES Water
- Source: The River Thames and River Lee, plus groundwater from beneath London
About 70% of London’s supply is drawn from the Thames upstream of Teddington Weir. Groundwater matters more in droughts. Which company supplies you, and so your local hardness, depends on your postcode. Greater London Authority: water (checked 2026-10-05).
How London compares
With an average of 272 ppm, London ranks 2nd hardest of the 19 cities in our directory, 206 ppm above the directory median of 66 ppm. Among the cities in our directory in Europe, Berlin is the hardest at 303 ppm and Manchester is the softest at 25 ppm.
What the range means
Published figures for London run from 247 to 302 ppm. The spread is relatively narrow (55 ppm), so the average is a reasonable guide, though your own tap can still differ from the citywide figure.
What very hard water means at home
Very hard water forms scale quickly on heating elements and in pipework, shortens the interval between descaling, and often leaves visible marks on glass and tiles. Appliance-level protection (salt, filters, scheduled descaling) is worth the effort, and some households consider a whole-home softener.
Appliance settings for 272 ppm water
- Dishwasher: salt yes; highest hardness band. Use dishwasher salt and verify the exact model setting in the manual.
- Coffee machine: descale every 4–6 weeks; filter: strongly recommended.
- Laundry: use the hard-water dose. Use the label maximum only for large or heavily soiled loads.
- Kettle: descale every 2–4 weeks.
- Humidifier: use demineralised or distilled water; clean every 3 days.
Frequently asked questions
How hard is the water in London?
The estimate for London, United Kingdom is about 272 mg/L as calcium carbonate (15.24 °dH, 27.2 °fH, 15.89 gpg), with a published range of 247–302 mg/L. That is classed as very hard water. City estimate; supplier zone varies by postcode.
Do I need dishwasher salt in London?
Yes. Use dishwasher salt and verify the exact model setting in the manual. Always follow your dishwasher manual.
How often should I descale a coffee machine in London?
At this hardness, descale every 4–6 weeks. Water filter: strongly recommended.
Do I need a water softener in London?
It is worth considering. At this level scale builds quickly, so a softener or filter system can reduce descaling and protect appliances. Check your appliance manuals first, as some limit softened-water use.
Is hard water in London safe to drink?
Water hardness is mainly an aesthetic and scale issue. The World Health Organization does not set a health-based guideline value for it. Hardness affects taste, scale and detergent use rather than drinking safety, and your utility is responsible for meeting drinking-water standards. If you have a specific health or dietary concern, ask your doctor.
Who supplies tap water in London?
Four companies: Thames Water (about 76% of Londoners), Affinity Water, Essex & Suffolk Water and SES Water. Source: The River Thames and River Lee, plus groundwater from beneath London.
How to check your own water
City averages are a starting point. To get your actual figure, look for the latest water-quality report from UK city water-quality study or your local supplier, or dip a hardness test strip in a glass of cold tap water and read it against the chart. Strips usually report in °dH, gpg or ppm; enter the number into the Waterdial checker to convert it and see the matching appliance settings. A manual reading always beats a city estimate.
Source
UK city water-quality study, checked 2026-10-05. Guidance is general; your appliance manual takes priority.
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