Descaling kettles and coffee machines in hard water.
Heating hard water leaves limescale: calcium carbonate that settles on elements, in boilers and inside pipes. The USGS notes that this scale can reduce the life of equipment, raise the cost of heating water, lower the efficiency of electric water heaters and clog pipes (source 6). This page collects what appliance makers say about how often to descale, so you can compare it with your own water on the city pages.
Kettles
These are the kettle manufacturers’ own statements:
| Manufacturer | What it says |
|---|---|
| De’Longhi (UK) | With particularly hard water, descale the kettle every month. In very soft water areas, every three months. (source 1) |
| Kenwood (UK) | The same: every month in particularly hard water, every three months in very soft water. It also warns that proprietary kettle descalers can damage the kettle’s surface finish, and to follow the instructions carefully. (source 2) |
| Smeg (South Africa) | In hard water areas, descale every 2 to 3 months. (source 3) |
So “monthly” is the shortest interval in these sources, quoted for particularly hard water, and the longest is three months. To see where your water sits, check your hardness against our bands: hard starts above 120 mg/L. None of these makers publishes a hardness threshold for kettles, so use these intervals as a guide and descale sooner if you see scale.
Coffee machines
Machines with a built-in boiler work in two ways: they ask you for your hardness, or they count water volume against the hardness you entered.
- De’Longhi. A test strip supplied with the machine is dipped in the water you use for daily coffee, and the squares show a level from 1 (low) to 4 (high). You enter that level in the menu, which determines how regularly the machine asks you to descale (source 4). A wrong setting means it will remind you at the wrong time.
- Nespresso Momento. The manual sets three hardness levels and descaling intervals in litres: 50 litres at high hardness, 150 at medium and 300 at low. It gives approximate times, shown below, and says to remove a fitted water filter before descaling (source 5).
- Philips drip coffee makers. Philips’s guidance assumes two full jugs of coffee a day and suggests descaling 2 or 3 times a year with soft water (up to 18 °dH) and 4 or 5 times a year with hard water (over 18 °dH) (source 7).
| Hardness setting | 25 recipes/day | 50 recipes/day | 80 recipes/day |
|---|---|---|---|
| High (C, 50 litres) | ~1 month | < 1 month | < 1 month |
| Medium (B, 150 litres) | ~3 months | ~2 months | ~1 month |
| Low (A, 300 litres) | ~6 months | ~3 months | ~2 months |
The pattern is the same across brands: the harder your water and the more you brew, the more often you descale, and the right hardness setting is what makes the reminder accurate. Hardness in °dH, mmol/L and ppm can be converted with our checker, which helps when a manual asks for a unit your water report does not use.
Practical points
- Find your number first. Look up your city on the hardness pages, or use a test strip. Hardness varies by supply zone, so a city figure is a starting point.
- Use the descaler your manual names. Kenwood warns about proprietary kettle descalers damaging the finish; follow your manufacturer’s instructions for the product and the rinse.
- Do not mix up TDS and hardness. A TDS meter reading is not hardness.
- A softener or filter changes the schedule. Softened water leaves less scale, but check your machine’s manual before using it; see softener sizing.
Sources
- De’Longhi UK. How do I descale my kettle?
- Kenwood. How do I descale my kettle?
- Smeg South Africa. FAQ: Kettles.
- De’Longhi US. How to check the water hardness before making a coffee?
- Nespresso. Momento Black Series user manual, “Descaling intervals”.
- US Geological Survey. Hardness in water: lime scale buildup inside a water pipe.
- Philips Australia. How often should I descale my Philips coffee maker?
We do not use retailer websites as sources. If a manufacturer has updated its advice, tell me. Related: Dishwasher settings by brand · Softener sizing · Water hardness by city.