Journal//3 min read
What we don't claim about water and coffee
We publish the hardness of your city's water, sourced from your utility and cited, and we recommend one of three blends on that basis. The water data is verifiable. The matching rule is our own editorial judgement: no peer-reviewed study validates a blend-to-water pairing, and one recent paper points in the opposite direction to ours. We would rather say that here than have you find it out elsewhere.
Every brand in this category makes a version of the same promise, and most of them dress an opinion in the language of science. We had a draft that did it too. This page exists because we took the drafts to the literature first, and the literature was less flattering than the marketing.
What is well supported
That water composition measurably changes how coffee tastes is not seriously in dispute. The SCA's own Water Chart is organised entirely around hardness and alkalinity and labels four distinct off-flavour outcomes. A 2021 study in Gıda found measurable differences in volatile compounds and trained-panel sensory scores across hardness levels. That much we are comfortable stating plainly.
What is contested
The mechanism usually given — that minerals change what is extracted from the coffee bed — has been tested and did not hold up well at realistic concentrations. A 2024 experimental study in Heliyon added calcium and magnesium at tap-water levels and found minimal variation in organic acids, and got similar results adding the salts after brewing as before. The authors place the interaction in the cup rather than in the extraction.
Water changes coffee. The popular explanation for why is not established. Both sentences are true, and most marketing copy only prints the first.
Where our rule is an opinion
Our pairing logic is compensatory: soft water gives a lighter cup, so we point you to a rounder blend. It is a coherent story. It is also unpublished. A 2025 paper in the Journal of Food Composition and Analysis reports the opposite arrangement — high hardness suiting darker roasts, low hardness suiting lighter ones — on a synergistic rather than compensatory logic. We have not been able to read that paper on a primary host, so we treat it as unverified rather than as a refutation. But we are not going to pretend it doesn't exist.
- We do not say our blends are scientifically proven to match your water. No such proof exists, for us or for anyone.
- We do not say a blend is optimised for a particular city. That would imply validation we have not performed.
- We do not claim any blend helps with limescale. Scale is calcium carbonate precipitating on hot metal; no roast profile touches it.
- We do not claim the SCA endorses our matching rule. They publish a handbook and a chart, and neither mentions us.
What we do stand behind
The city water figures, and the fact that we cite the utility that published each one. A city is not homogeneous — Naples runs from about 11 °dH in Vomero to about 43 °dH in Ponticelli, which is why we split it by district rather than publishing a meaningless average — and household filtration scrambles it further. Where we cannot verify a figure, the city does not go online at all.
If that sounds like a smaller claim than our competitors make, it is. It is also the one we can still defend after you have checked it.
Questions this raises
- Is matching coffee to water hardness scientifically proven?
- No. Water composition measurably affects taste, but no peer-reviewed study validates a specific blend-to-water matching rule. A 2025 paper suggests hard water may suit darker roasts, which is the opposite of the compensatory logic most brands including ours use.
- Can a coffee blend reduce limescale in my machine?
- No. Limescale is calcium carbonate precipitating when carbonate-hard water is heated. No roast profile, origin or grind size affects it. Descaling and water treatment are the only levers.