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Water knowledge

Drinking hard water: safe – what hardness really means

White deposits in the kettle, dull marks on glasses: around the house, hard water has a dubious reputation. In the glass it deserves none, because what we call “limescale” is dissolved calcium and magnesium, two minerals the body needs every day. Reason enough for a closer look at water hardness and the Swiss scale that measures it.

Updated August 2026 · 6 min read

In brief

  • What we call “limescale” is dissolved calcium and magnesium — two minerals the body needs daily.
  • Hardness is stated in French degrees (°fH) and is not a defect in quality.
  • The kettle furs up because heating precipitates lime; in the body the minerals stay dissolved.

What exactly is limescale in water?

Water is a good solvent. On its way through soil and rock it picks up minerals; in layers of limestone and dolomite, above all calcium and magnesium. These two elements determine what is known as water hardness: the more of them dissolved, the “harder” the water. Regions with limestone bedrock therefore tend to have hard water, while regions with granite or gneiss tend towards soft water.

Strictly speaking, the term “limescale” is imprecise here. No particles of lime float in the water; what it carries are invisibly dissolved calcium and magnesium ions, mostly accompanied by hydrogen carbonate. Only when the water is heated or evaporates do these components combine into solid calcium carbonate – the white coating familiar from the kettle.

How is water hardness measured, and what does °fH mean?

In Switzerland, water hardness is stated in French degrees of hardness (°fH); one degree corresponds to 10 milligrams of calcium carbonate per litre. In Germany, German degrees of hardness (°dH) are customary; one °dH corresponds to around 1.8 °fH. The usual Swiss classification is as follows:

  • 0 to 7 °fH: very soft
  • 7 to 15 °fH: soft
  • 15 to 25 °fH: moderately hard
  • 25 to 32 °fH: fairly hard
  • 32 to 42 °fH: hard
  • above 42 °fH: very hard

How hard your tap water is depends on the local geology and varies widely across Switzerland – from the soft water of alpine crystalline regions to the hard water of many municipalities on the Swiss Plateau. The water utilities publish the hardness of their networks; the figure is often found directly on the municipality's website.

Water hardness in French degrees (°fH)

0715253242
  • 0–7 very soft
  • 7–15 soft
  • 15–25 medium
  • 25–32 fairly hard
  • 32–42 hard
  • 42–50 very hard

Your value: 18 °fH — medium

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The classification of water hardness in French degrees, as commonly used in Switzerland.

Is hard water bad for you?

The short answer: no. Calcium and magnesium, the very substances that make water hard, are essential minerals. The body needs both every day, among other things for bones, muscles and the nervous system. Professional bodies such as the German Nutrition Society cite reference values for adults of around 1,000 mg of calcium and, depending on age and sex, roughly 300 to 400 mg of magnesium per day.

Mineral-rich water can contribute to this supply, since calcium and magnesium from water are considered readily available to the body. Nor does drinking-water legislation set any health-based upper limit for water hardness: hard water is safe to drink without restriction. Incidentally, the hydration calculator shows how much fluid makes sense for you personally.

This article provides general information on water hardness and minerals; it is no substitute for medical advice. If you have questions about your own mineral intake or are experiencing symptoms, it is best to consult a doctor.

Why does limescale build up in the kettle, but not in the body?

The worry seems obvious: if hard water scales up machines, what does it do inside the body? The answer lies in the chemistry. Scale forms because, on heating, dissolved calcium hydrogen carbonate breaks down and precipitates as solid calcium carbonate. That is a purely physical and chemical process in a passive system: a heating element can neither absorb the mineral nor release it again.

The human body is not a water pipe. Calcium and magnesium are absorbed in the gut in a controlled way, their levels in the blood are finely regulated by hormones, and what the body does not need, it excretes again. Hard water you drink therefore leaves no “deposits” behind. That notion comes from household experience, not from physiology.

Why is mineral content a mark of quality in mineral water?

With natural mineral water, at the latest, the perspective turns around completely: here, the content of dissolved minerals is part of the water's identity. Natural mineral water must come from a protected underground source, be of original purity and show a largely constant composition, which is why the mineral values appear on every label. Exactly how the categories differ is explained in our article on spring water and mineral water.

An example from the Sardona Alps: the naturally alkaline mineral water of Piz Sardona (pH 8.0) seeps into the ground at over 2,000 m above sea level by the UNESCO World Heritage Tectonic Arena Sardona and filters through layers of rock and stone for around 12 years before being drawn from the Castels spring in Mels. Along the way it takes up 87 mg of calcium, 35 mg of magnesium, 265 mg of sulphate and 133 mg of hydrogen carbonate per litre, 540 mg of dissolved minerals in total. On paper, such a water sits well within the “hard” range — that hardness is simply the result of the long passage through the rock.

What counts as a drawback around the house is, in the glass, simply mineral content gathered on a long journey through the mountains. You will find more about the origin and analysis of the Castels spring under our water.

Frequently asked questions

How do I find out how hard my tap water is?

The water utilities provide information on the quality of their drinking water and usually also publish its hardness in °fH, most often on the website of the municipality or the utility. The figure is practically useful, too: detergent, for instance, is dosed according to water hardness, and many appliances can be set to the local hardness.

Can hard water be softened – and is that necessary?

Technically it is possible, for instance with ion exchangers, which usually swap calcium and magnesium for sodium. To protect household appliances, that can be worthwhile. For drinking, there is no reason to soften water; on the contrary, it strips out precisely those minerals that make the water nutritionally interesting.

Does hard water taste different from soft water?

Yes. Dissolved minerals shape the taste: harder, more mineral-rich water often comes across as fuller and slightly astringent, while soft water tastes more neutral. Hardness also plays a part in coffee and tea, because it influences how the aromas are extracted; baristas therefore pay close attention to the composition of their brewing water.

What does carbonate hardness mean, as opposed to total hardness?

Total hardness covers all dissolved calcium and magnesium. Carbonate hardness is the part of it bound to hydrogen carbonate: it can precipitate as calcium carbonate when heated and is therefore responsible for scale. The rest, known as permanent hardness, remains dissolved even when the water boils.

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Alkaline mineral water with a pH of 8.0 from the Castels spring in Mels — filtered through the rock of the Sardona Alps for twelve years.

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