Descale a coffee machine when its indicator tells you to, and set the machine’s hardness setting to match your water. As a rough rule, soft water (under 60 mg/L, about 3.5 gpg) may need descaling a few times a year at most. Very hard water (over 180 mg/L, about 10.5 gpg) can need it every month or two. Your manual overrides every number on this page.
Find your own figure first. Enter your ZIP or postcode on the lookup page, or open your city page from the list below. The calculator converts between mg/L, gpg, °dH and °fH if your machine uses a different unit.
Why hardness sets the schedule
Heating hard water turns dissolved calcium and magnesium into solid calcium carbonate. The USGS notes that deposits form when hard water is heated, for example in a home water heater. A coffee machine has the same problem on a small scale. The boiler, the thermoblock and the narrow tubes are the hottest surfaces, so scale builds there first.
Scale does three things to a machine. It slows the flow of water. It insulates the heating element, so heat-up takes longer. In bad cases it blocks a valve or a pipe. We have no independent test that puts a number on energy loss or lifespan for coffee machines, so we make no such claim.
De’Longhi, one major maker, says that how often you need to descale depends mainly on your water hardness and how often you brew. That matches what most manuals say.
Descaling interval by hardness band
The bands below are the USGS classes, with gpg converted at 17.1 mg/L per grain. The intervals are our rule of thumb for a household making a few cups a day. They are not manufacturer specifications.
| Hardness class | mg/L as CaCO₃ | gpg | Typical interval if you have no indicator |
|---|---|---|---|
| Soft | 0–60 | 0–3.5 | Every 6 months, or when output slows |
| Moderately hard | 61–120 | 3.6–7.0 | Every 3 to 4 months |
| Hard | 121–180 | 7.1–10.5 | Every 2 to 3 months |
| Very hard | over 180 | over 10.5 | Every 1 to 2 months |
Treat the right-hand column as a starting point. A machine used for ten cups a day scales faster than one used for two. A machine that you leave with water in the tank for days also gives scale more time to settle.
A Swiss coffee retailer gives a similar hardness-based rule of thumb in °dH and suggests descaling every two to three months even without a warning light. That is a retailer’s advice, not a manufacturer’s, so use it only as a cross-check.
Indicator first, calendar second
Most automatic machines count brews and water volume and light a descale warning. That warning is more reliable than any calendar, but only if the hardness setting is right. If you set the machine to “high” in an area with soft water, it will ask for descaling far too often. De’Longhi support pages say this directly: if the descale light flashes frequently, check that the hardness setting matches your water.
To set it, you need your hardness. Look up your city, or use the test strip that often ships with the machine. Utility reports and our city pages give citywide figures, and some cities have several supply zones, so the figure at your tap can differ.
What the numbers look like in real cities
These are the medians in our data. Each page shows its source and date.
- Boston: 13.1 mg/L. Very soft. Descaling is a rare job.
- New York and Charlotte: 32 mg/L each. Soft.
- Houston: 110 mg/L. Moderately hard.
- Los Angeles: 128 mg/L. Hard, at the low end of the class.
- Essen: 117.8 mg/L. Moderately hard, just under the hard line.
- Phoenix: 237 mg/L. Very hard. This figure is computed rather than measured, so check the page for the method.
- Las Vegas: 280 mg/L. Very hard.
- Indianapolis: 317 mg/L. Very hard.
- Berlin: 328.4 mg/L. Very hard, with a range across supply zones.
Two people in the same metro area can land in different bands. Where a page shows a range, use the figure for your address, not the median.
Descaling basics that apply to most machines
- Use the descaler your manufacturer names. De’Longhi states that an unsuitable descaler, or a wrong procedure, may cause faults that its guarantee does not cover. Other makers set similar conditions.
- Run the full cycle, then rinse the tank and run clean water through until the descaler taste is gone. Follow the manual for the number of rinses.
- Do not mix descalers or use vinegar unless the manual allows it. Some manuals warn against vinegar, and we have no independent data on its effect on seals.
- Descale a milk frother or steam wand according to its own instructions. Milk residue is a separate cleaning job from scale.
Slowing scale instead of removing it
In hard and very hard areas, a filter cartridge in the tank is the usual first step. Many makers sell filters for their own models and say they slow scale formation. We have no independent test data for them, so we quote no performance figure. A whole-house softener removes calcium and magnesium for every tap. It needs salt, a drain and some space. The calculator will size one from your hardness and household size.
If you use bottled or softened water in a machine, check the manual. Very soft water is not always recommended for machines with conductivity sensors. The sensor may not detect the water level correctly. This varies by model.
FAQ
Can I skip descaling if my water is soft? No. Soft water slows scale but does not stop it, and the machine’s own warnings still apply. In a very soft city like Boston you may descale only once or twice a year, but follow the indicator.
My machine asks for descaling every few weeks. Is that normal? In a very hard area such as Indianapolis or Berlin, it can be. If your water is soft or moderate, check the hardness setting first. A setting that is too high is a common cause of frequent prompts, according to De’Longhi support.
Is the table the same for espresso machines and pod machines? Not exactly. Pod machines hold less water but heat it through narrow channels, and espresso machines with a boiler hold more. Both are sensitive to scale. Use the table as a guide and read your own manual for the exact cycle.
Sources
- USGS, Water Science School, Hardness of water: https://www.usgs.gov/special-topics/water-science-school/science/hardness-water
- De’Longhi, How to descale a coffee machine: https://www.delonghi.com/en-us/e/r/descale-coffee-machine
- De’Longhi support, Descale light is flashing frequently: https://support.delonghi.com/en/dinamica-plus/Descale-light-is-flashing-frequently-50a2
- Kaffeemacher, De’Longhi Dedica descaling (retailer, used as cross-check only): https://kaffeemacher.ch/en/blog/delonghi-dedica-entkalken
- City figures: source pages linked from each city page, for example Boston and Berlin.