Water knowledge

What is alkaline water?

Alkaline water has a pH above 7 – so much for the simple definition. What is more interesting is where that value comes from: minerals the water dissolves from the rock, above all hydrogen carbonate. And because alkaline water is often sold with big promises, let us say it up front: your body regulates its own acid-base balance, no matter what you drink.

Updated August 2026 · 6 min read

The pH scale: neutral, acidic, alkaline

The pH value indicates how many free hydrogen ions a liquid contains. The scale runs from 0 to 14: at 7 a solution is neutral, below that acidic, above it alkaline. Lemon juice sits at around pH 2, coffee at 5, a baking-soda solution at just over 8, soapy water at around 9. One thing matters: the scale is logarithmic. Water with pH 8 contains ten times fewer free hydrogen ions than water with pH 7 – chemically a clear difference, in taste barely one.

In Switzerland, drinking water mostly falls between pH 7 and 8.5. Carbonated mineral water is considerably lower, often around pH 5, because dissolved carbon dioxide forms carbonic acid in the water. Still water from limestone-rich rock, by contrast, reaches values of around 7.5 to 8.

What determines the pH value of water?

Chemically pure water would be exactly neutral. Natural water practically never is, because it dissolves substances from air and rock along its way. Two of them shape the pH value in particular: carbon dioxide lowers it, because it reacts to form carbonic acid in water. Hydrogen carbonate raises it and buffers it at the same time; the value therefore stays stable even when small amounts of acid are added.

Where the hydrogen carbonate comes from is decided by geology. Limestone and dolomite release calcium, magnesium and hydrogen carbonate on contact with water; such water becomes hard and, at the same time, slightly alkaline. Silicate rock such as granite releases very little, so the water stays soft and its pH value weakly buffered. To see how closely rock and water hardness are linked, read the article on calcareous water.

Naturally alkaline or artificially ionised?

Naturally alkaline water forms slowly. Seepage water travels through layers of rock, dissolving minerals along the way, and reaches the spring with a composition that barely changes over the years. Here, the pH value is a consequence of the mineralisation, not a target that has been dialled in. One example is the Castels spring in Mels, whose water emerges from the mountain with a natural pH of 8.0.

Water ionisers take the opposite route. These devices use electrolysis to split tap water into an alkaline and an acidic stream; the alkaline one is drunk, the acidic one goes down the drain. The pH value produced this way can reach 9 or more, but it is weakly buffered and falls again as soon as the water absorbs carbon dioxide from the air. To find out what lies behind these devices and how to put their sales promises into perspective, read the article on Kangen water.

Does alkaline water de-acidify the body?

No. The body keeps the pH of the blood within a narrow window between 7.35 and 7.45 on its own. Several systems work together to do so: buffer substances in the blood intercept acids immediately, the lungs breathe out carbon dioxide, and the kidneys excrete excess acids in the urine. This regulation runs around the clock, regardless of what you drink.

Then there is the stomach. Gastric acid has a pH of roughly 1.5 to 2; every glass of water first meets this strongly acidic environment. The idea that alkaline water could “de-acidify” the body does not stand up to this physiology. A genuine shift in the acid-base balance, such as acidosis, can be a medical emergency and belongs in the hands of a doctor.

If you have questions about your acid-base balance, or if you have an existing kidney or metabolic condition, it is best to discuss your drinking and eating habits with your doctor.

Why do people drink alkaline water anyway?

For two understandable reasons: taste and mineralisation. Water rich in hydrogen carbonate tastes mild and soft, since the tart freshness of carbonic acid is absent and the minerals come through in the taste. Those who prefer their water without bubbles anyway therefore often end up with a still water that is naturally slightly alkaline.

Mineralisation is the second reason. Water from limestone-rich rock brings calcium and magnesium with it, two minerals the body needs every day. The European Food Safety Authority (EFSA) gives as a reference for adults aged 25 and over 950 mg of calcium per day, along with 350 mg of magnesium for men and 300 mg for women. A mineral-rich water contributes to this intake without a single calorie.

Twelve years in the mountain instead of seconds in a device: that is how long the water of the Castels spring takes to travel from its infiltration area at over 2,000 m above sea level in the Sardona Alps, at the UNESCO World Heritage Tectonic Arena Sardona, to the spring catchment in Mels. On this journey through layers of rock and stone it takes on its natural pH of 8.0, together with a total of 540 mg of minerals per litre, including 87 mg of calcium and 35 mg of magnesium. You will find all the values in detail on the water page.

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