Water hardness in La Rochelle
Tap water in La Rochelle measures 27.7 °f.
France classes that as moyennement dure, meaning moderately hard. On the internationally comparable scale, from the WHO and the US Geological Survey, that is very hard.
How hardness is classified
There is no European classification; each country sets its own bands. Here is how the country itself classifies it, and how the international scale compares:
How France classifies it
Internationally, from the WHO and the US Geological Survey
Does the figure apply at your address?
Probably, but not certainly. A utility publishes one figure for a supply zone, and a large city is rarely one zone. Buildings with their own softening plant differ again.
The figure for your address or postcode is available directly from Hubeau, Ministère de la Santé (contrôle sanitaire) — and it is often printed on the water bill too.
A hardness test strip from a chemist or hardware shop costs a few euros and settles it in a minute. That is also the only way to know what comes out of your own tap rather than what leaves the waterworks.
Setting an appliance
A dishwasher, washing machine or coffee machine that asks for a level from 1 to 4 wants 3 here.
That four-level scale is the one German detergent law used until 2007. The law moved to the three bands above; the dials did not.
The same figure on other scales
15.5 °dH · 27.7 °f · 2.77 mmol/l · 277 mg/L
Dishwashers and washing machines ask for hardness in different units depending on where they were sold: millimoles per litre in Germany, degrees in Austria and Switzerland, parts per million in Britain. It is one quantity read on four scales.
What it means day to day
Very hard water leaves a lot of limescale. Kettles, coffee machines and shower heads scale up markedly faster, detergent needs a higher dose, and anything with a heating element is worth descaling regularly.
Hard water is not a fault
Hardness is not a safety question. Hard water is fine to drink; it just leaves more limescale.
The calcium and magnesium that make water hard are the same minerals a diet needs, and drinking water counts towards the daily intake of both. The WHO reviewed how much in Calcium and magnesium in drinking-water.
A thin carbonate layer on the inside of a pipe also protects the metal underneath from corroding. Water softened to nothing is harder on plumbing, not easier.
The water is fine to drink either way: Is the tap water in La Rochelle safe to drink?
How it compares
Of the 59 cities in France with a published figure here, La Rochelle is the 16th hardest. The middle of the range sits at 22.3 °f.
The softest is Ajaccio at 6.0 °f, the hardest Antibes at 40.2 °f.
Where the figure comes from
Published by Hubeau, Ministère de la Santé (contrôle sanitaire), as of 18 June 2026.
The figure is total hardness, which counts every calcium and magnesium compound in the water. Some utilities also publish carbonate hardness, the part bound to carbonic acid, which is the share that forms limescale when the water is heated.