How to test your water hardness (and what the numbers mean for espresso)
Every maintenance question about espresso machines eventually lands on the same unknown: how hard is your water? It decides your descaling interval, your filter's lifespan and half the difference between a machine that lasts five years and one that lasts fifteen. The good news: finding out takes thirty seconds and a few euros.
Three ways to find out
- Test strips — the practical answer. Dip a strip in your tap (or tank) water, wait, compare colours. Dedicated hardness strips or aquarium GH strips both work; you need a band, not a lab figure.
- Your water utility's report — most utilities publish hardness per postcode. Look for °dH (German degrees), °f (French degrees) or ppm as CaCO₃, and use the table below to translate.
- The kettle heuristic — white crust in your kettle within a few weeks means hard to very hard. No crust after months of daily use means soft to medium. Free, and honest enough to start with.
The conversion table
| Band | °dH | °f | ppm CaCO₃ | In the Espremo app |
|---|---|---|---|---|
| Soft | 0–4 | 0–7 | 0–70 | Soft (RO, distilled, low-mineral bottled) |
| Medium | 4–8 | 7–14 | 70–140 | Medium (filtered tap, most bottled) |
| Hard | 8–14 | 14–25 | 140–250 | Hard (untreated tap, hard-water area) |
| Very hard | 14+ | 25+ | 250+ | Very hard (known hard area, no filtration) |
Rule of thumb for converting: 1 °dH ≈ 17.8 ppm CaCO₃, and 1 °f = 10 ppm. If your utility quotes millimoles per litre, multiply by 100 to get ppm.
What to do with the number
Feed it into the descaling interval calculator and it becomes a schedule: descale cadence per machine type, and if you run a softener or filter, the replacement interval that keeps it true. Two edge notes: brewing on RO or distilled water is gentle on scale but can taste flat and confuses some level sensors, and if you soften your water later, remember the schedule changes with it — update the bucket in the app and everything recalculates.
Frequently asked questions
What is the easiest way to test water hardness at home?
Test strips. A pack costs a few euros, works in thirty seconds (dip, wait, compare colours) and is accurate enough to pick a maintenance schedule. Aquarium GH strips work fine for this purpose.
What water hardness is best for espresso machines?
Machines are happiest around soft to medium hardness: enough minerals for extraction and sensor function, not enough to scale quickly. Very soft (RO or distilled) can be hard on boilers and bland in the cup; very hard water is a scale factory.
How do I convert dH to ppm?
One German degree (1 dH) is about 17.8 ppm CaCO3. So 7 dH is roughly 125 ppm, and 14 dH is roughly 250 ppm. French degrees are simpler: 1 f = 10 ppm.
Never miss this task again
Espremo is a free iPhone app that builds a maintenance schedule for your exact machine — covering 108 models — and taps you on the shoulder when something is due.
Download on the App Store