Water hardness and your coffee machine: a UK guide

The short answer

1. Find your number. Your water company publishes the hardness of your supply, usually by postcode, in mg/l as calcium carbonate (CaCO3).
2. Tell the machine. Many bean-to-cup machines store a hardness level and use it to time the descaling alert.
3. Decide on a filter. In hard water areas, an in-tank filter trades descaling for filter changes. In soft water areas there is little for it to do.

The rest of this page gives the conversion table, what the manuals say about hardness settings and filters, and what the public sources say about softeners and jug filters.

What hardness is, and why a coffee machine cares

Hardness is dissolved calcium and magnesium, picked up as water passes through chalk and limestone. When hard water is heated, part of it is deposited as scale. United Utilities’ fact sheet separates two components: temporary (carbonate) hardness, which forms scale when water is heated or boiled, and permanent hardness, which does not (Water hardness).

A coffee machine heats a small amount of water for every cup, so it is exactly the kind of appliance where scale collects. The Drinking Water Inspectorate (DWI), the regulator for England and Wales, says hard water causes scaling in hot water systems, kettles and domestic appliances, and that scale shortens their life and reduces their efficiency. It also notes that the regulations set no standard for hardness, calcium or magnesium: hard water is a nuisance for appliances, not a breach of drinking water quality (Water Hardness / Hard Water).

The bands, in every unit your manual might use

The DWI describes hardness in five bands, in mg/l as calcium carbonate. Appliance manuals written for several countries often ask for Clark (English), German or French degrees instead. We have converted the DWI’s band limits using the factors United Utilities publishes: multiply mg/l by 0.07 for Clark degrees, by 0.056 for German degrees and by 0.1 for French degrees.

DWI description	mg/l as CaCO3	Clark degrees	German degrees	French degrees
Soft	up to 100	up to 7	up to 5.6	up to 10
Slightly hard	100 to 150	7 to 10.5	5.6 to 8.4	10 to 15
Moderately hard	150 to 200	10.5 to 14	8.4 to 11.2	15 to 20
Hard	200 to 300	14 to 21	11.2 to 16.8	20 to 30
Very hard	more than 300	more than 21	more than 16.8	more than 30

The conversions are our arithmetic; the bands and the factors are the sources’. One Clark degree is therefore about 14.3 mg/l.

The DWI also passes on a World Health Organization reference point that is useful for coffee machines: water at 200 mg/l or more will produce scale.

Where to find your figure

• Your water company. The DWI says to contact your water company for an accurate figure, since local variation does not show on a national map. United Utilities, for example, gives the hardness of your supply when you enter your postcode on its water quality page. Check your own company’s website for the equivalent.
• The DWI’s map of typical hardness covers England and Wales and gives the broad picture. As one regional example, United Utilities says most water in the North West is soft or very soft, because it comes from upland reservoirs.
• The strip in the box. De’Longhi supplies a hardness strip with many of its bean-to-cup machines; its UK support page describes it as the way to find the level to set (How do I set the water hardness on my fully auto coffee machine?). The strip gives a level from one to four, not a figure in mg/l.

Setting the machine: the step most people skip

The hardness level is what the machine uses to decide when to ask for descaling. De’Longhi’s Magnifica Evo manual says so directly: setting the water hardness lets the machine light the descale indicator according to the actual hardness of the local supply (ECAM29X.6Y - 29X.8Y EX:1 Bean to cup espresso and cappuccino machine, Instructions for Use). The procedure it describes:

1. Dip the strip fully in a glass of water for about one second.
2. Take it out and shake it lightly.
3. After about a minute, one to four red squares appear. Each square corresponds to one level.
4. Store that level in the machine’s settings menu.

De’Longhi’s UK support page calls this an important step in determining when the machine needs to be descaled. The reasoning cuts both ways:

• Hard water, machine set too low: the alert comes late, and scale has longer to build up.
• Soft water, machine set too high: the alert comes early, and you spend descaler and 30 to 45 minutes you did not need to.

How the levels are stored differs from model to model, so follow your manual. The Evo manual labels the four levels low, medium, medium/high and high, without figures in mg/l: on that machine it is the strip, not the water company’s number, that selects the level. The water company’s figure remains the better guide to how much scale to expect and whether a filter is worth having.

Filters: three kinds, three different jobs

In-tank cartridges from the machine’s maker

These sit in the water tank and treat only the water the machine uses. The makers state their life as follows:

Filter	Stated life	What the maker claims
Philips AquaClean	change when the machine prompts, up to 625 cups per filter	up to 5,000 cups without descaling, based on eight filter changes; the real figure depends on the drinks chosen and on rinsing and cleaning patterns
De’Longhi water softener filter	about two months in normal use; three weeks at most if the machine stands unused	no cup figure given
Sage water filter (the Bambino)	three months or 40 litres	changing it on schedule reduces the need to descale

Sources: Calc and Water filter CA6903/10, Philips Series 2200 Fully automatic espresso machines EP2220/14, ECAM11.1XX - 12.1XX - 20.1XX - 21.1XX - 22.1XX Bean to cup espresso and cappuccino machine, Instructions for Use and the Bambino BES450/SES450 EN Quick Guide.

Two rules apply across brands. The filter comes out before descaling: Philips and De’Longhi both say so. And an old filter does not keep working because the machine has been idle: De’Longhi’s three-week limit for an unused machine is the clearest statement of that.

Jug filters

The DWI says that some jug filters contain ion-exchange resin beads that alter the temporary hardness of the water, so that they may reduce scale in a kettle, and adds that they do not alter the permanent hardness. Whether filling a coffee machine from a jug reduces how often it asks for descaling is not something the manuals we read address.

Household water softeners

A softener treats the whole supply or the hot water side. The DWI’s advice is to keep an unsoftened outlet for drinking water, because softened water contains more sodium, which matters for premature babies and for people on low-sodium diets. It also warns that softened water may be more aggressive to plumbing. On magnetic and similar devices, the DWI is brief: they do not soften the water.

Is a filter worth it? A way to decide

Filters and descaler are two ways of paying for the same thing. A rough rule, using the DWI’s bands:

• Soft or slightly hard (up to 150 mg/l): set the level, descale when asked, and a filter is optional. The alert will be infrequent.
• Moderately hard (150 to 200 mg/l): either approach works. Compare a year of filters with a year of descaler at your own prices.
• Hard or very hard (200 mg/l and above): this is the range the WHO reference point describes as scale-forming. Expect frequent alerts without a filter, and factor filters into your running costs from the start.

To put numbers on it, count filters per year (six for De’Longhi’s two-month filter, four for Sage’s three-month one), multiply by what you pay, and divide by your cups per year. Our guide to the real cost of a cup walks through that sum, and the calculator below gives you the coffee and machine share to add it to.

How this affects which machine you buy

Less than you might think. Every bean-to-cup machine in our comparison has to be descaled, and the tank sizes are close: 1.8 l on the Philips 2200 and 1.8 l on the De’Longhi Magnifica S, for instance. What differs is the consumables each brand asks for, which we cover in the cleaning guide, and the descaling routine itself, covered in how to descale a bean-to-cup machine.

If you live in a hard water area and have not yet chosen, the machine finder will narrow the field on everything else, and hardness becomes a line in your running costs, not a reason to pick one model over another.