No, not all water is the same. Two glasses that look identical can differ by a factor of fifty in dissolved minerals. Water picks up calcium, magnesium, sodium, bicarbonate, sulfate and chloride from the rock it travels through, and that mixture decides three things: how the water tastes, whether it leaves limescale in your kettle, and how much of your daily calcium and magnesium you get simply by drinking. In some regions two litres of tap water covers a meaningful share of your magnesium reference intake. In others it contributes almost nothing.
This article explains what is actually dissolved in your water, what hardness means (and what it does not mean), why mineral content changes taste in a predictable way, and what the research does and does not support about health. It is the companion piece to our guide on whether you can safely drink tap water everywhere in Europe.
What is actually dissolved in drinking water
Rain that falls on granite stays soft. Rain that filters through chalk or limestone dissolves calcium and bicarbonate on the way down. Gypsum adds sulfate. Marine sediments and road salt add sodium and chloride. Dolomite adds magnesium. By the time water reaches a spring or a well, it carries a chemical signature of the ground it passed through.
The sum of everything dissolved is called total dissolved solids (TDS), usually reported in milligrams per litre. Water treatment labs also report the individual ions, because two waters with the same TDS can be chemically very different: one dominated by calcium and bicarbonate, another by sodium and chloride. As you will see, that difference is exactly what your tongue notices.
Conductivity is often printed instead of TDS. It measures how well the water conducts electricity, which rises with dissolved ions, so it works as a fast proxy for total mineral load.
What hardness actually means
Hardness is not a measure of purity, cleanliness or quality. It is the combined concentration of calcium and magnesium, conventionally expressed as milligrams per litre of calcium carbonate equivalent (or in German degrees, French degrees and other local units, which is why the same water can be described with four different numbers).
Hard water is why your kettle scales, your shower screen spots and your soap lathers poorly. Soft water does none of that, which is convenient, but softness is not a health credential. Both extremes have practical consequences: very low calcium and magnesium can make water more aggressive toward pipes, and very high levels cause scaling and taste complaints. This is the reason the World Health Organization published a dedicated background document on hardness for its drinking water guidelines, alongside a separate report on the public health significance of calcium and magnesium in drinking water.
One thing worth knowing about European regulation: the EU Drinking Water Directive itself sets no limit values for hardness, calcium or magnesium. A 2020 review in Regulatory Toxicology and Pharmacology found that member states fill the gap themselves, with 12 countries regulating these parameters in law and 7 more through technical guidance, and concluded that most of those national rules are not based on current research and are not comparable with one another. So a label saying your water is "within norms" tells you very little about its mineral profile.
Why the same tap can taste different from the bottle
Taste is where mineral content stops being abstract. Two Spanish studies mapped this carefully.
In a 2013 study in Water Research, trained panellists blind tasted twenty bottled mineral waters and twenty five tap and bottled samples, rating overall liking from 0 to 10 against thirteen measured physicochemical parameters. The preferred samples had moderate total dissolved solids together with relatively high bicarbonate, sulfate, calcium and magnesium, and a relatively high pH. High sodium, potassium and chloride were scored low. Residual chlorine did not affect the ratings, although it did let the panel tell tap water from bottled mineral water.
A 2017 follow up in Talanta repeated the exercise with sixty nine untrained volunteers and twenty five waters, and reached the same conclusion with ordinary drinkers: people preferred waters rich in calcium, bicarbonate and sulfate over waters rich in sodium chloride. The team could even predict overall liking from the mineral analysis alone.
The practical translation: "flat" or "dull" water is usually very low mineral water. Water that tastes salty or slightly metallic is usually sodium and chloride dominant. Water many people describe as fresh and clean tends to sit in the middle, with calcium and bicarbonate leading. Temperature matters too, which is one reason a bottle that stays properly cold, like our double wall insulated MAGBOTL, changes the drinking experience without changing the chemistry.
How much of your mineral intake comes from water
More than most people assume, and with enormous variation.
A study in the Journal of General Internal Medicine collected mineral analysis reports from municipal water authorities in 21 major North American cities and compared them with bottled waters and with dietary reference intakes. For half of the tap water sources examined, adults drinking two litres a day would cover between 8 and 16 percent of the calcium reference intake and between 6 and 31 percent of the magnesium reference intake. European bottled waters generally carried higher mineral levels than North American tap water or North American bottled water.
The French SU.VI.MAX cohort put numbers on the spread between brands. Regular drinkers of a calcium and magnesium rich mineral water were consuming water at 486 mg/L calcium and 84 mg/L magnesium. A moderately mineralised water supplied 202 mg/L and 36 mg/L. The low mineralised waters in the same study contained just 9.9 to 67.6 mg/L calcium and 1.6 to 2 mg/L magnesium. Same shelf, same price bracket, roughly fifty times the magnesium in one bottle versus another.
That spread is global. A 2021 analysis in the Journal of Clinical Medicine read the labels of bottled waters in two major supermarkets across 21 countries and found that mineral composition varies enormously: median bicarbonate levels differed by factors of 12.6 for still and 57.3 for sparkling water, and median calcium by factors of 18.7 and 7.4 respectively.
Hardness and health: what the evidence supports
This is where honesty matters more than a good story. The association between harder water and lower cardiovascular mortality has been studied for decades. A 2023 systematic review with meta analysis in Foods found that 17 of 25 qualitatively analysed studies reported a significant relation between total water hardness and protection from cardiovascular mortality, and the quantitative analysis pointed the same way. The authors also stated plainly that heterogeneity was high, confounding factors were many, and more research is needed.
That is the correct level of confidence: a consistent ecological signal, not a proven causal effect, and certainly not a reason to treat any water as a treatment. A broader review in the International Journal of Preventive Medicine reaches a similar conclusion across a wider set of outcomes. Water hardness is one small factor among diet, activity, genetics and healthcare access.
Filters, softeners and reverse osmosis: what each one changes
Filtration is not one thing, and the differences matter for minerals.
- Activated carbon (jug filters, tap filters, fridge cartridges) mainly targets chlorine, taste and odour compounds and some organics. It has limited effect on dissolved calcium and magnesium, so hardness largely survives.
- Ion exchange softeners do not remove hardness minerals in the ordinary sense: they swap calcium and magnesium for sodium. Your kettle benefits, your mineral intake from water drops and sodium rises, which is the opposite direction from what tasting panels prefer.
- Reverse osmosis pushes water through a semi permeable membrane and removes most dissolved solids. A 2023 narrative review in Cureus reports that RO systems remove roughly 92 to 99 percent of minerals including calcium and magnesium along with contaminants. The same review argues that habitual consumption of very low mineral water may work against bone and dental mineral density. Treat that mechanism as a hypothesis rather than settled fact: it is a narrative review, not a controlled trial. What is not in doubt is the first part: RO water contains almost no calcium or magnesium unless you put them back.
The regulatory review mentioned earlier makes the same point from the policy side: increasing volumes of drinking water are now produced by desalination, which disturbs the natural mineral composition. That is why several countries recommend remineralisation after such treatment.
Does mineral water replace a magnesium supplement?
Water is a genuine source of magnesium, and a well absorbed one, but the arithmetic decides whether it is a meaningful source for you.
Two controlled studies are useful here. In a randomised crossover trial published in Forschende Komplementärmedizin, 22 healthy men drank 500 ml of mineral water containing 281 or 120 mg/L magnesium, or a low magnesium control water at 8 mg/L, or took a magnesium capsule. Serum magnesium changes over the first four hours differed significantly between conditions, confirming that magnesium in water is absorbed rather than passing through.
The second study is arguably more practical. In a stable isotope trial in the British Journal of Nutrition, twelve healthy men drank 1.5 litres of magnesium rich mineral water, delivering the same 126 mg of magnesium, either as two servings of 750 ml or as seven servings of about 212 ml spread through the day. Spreading it out raised fractional absorption from 32.4 percent to 50.7 percent and retention from 29.0 to 47.5 percent. Sipping beats gulping, for water and for anything dissolved in it.
So: if your tap or bottled water sits at 80 mg/L magnesium and you drink two litres, water alone contributes a substantial part of your daily magnesium. If your water contains 2 mg/L, it contributes essentially nothing and the rest has to come from food, or from a supplement such as our Magnesium 7 in 1. Magnesium contributes to normal muscle function, to normal functioning of the nervous system and to the reduction of tiredness and fatigue. Which form you choose still matters, and we cover that in which form of magnesium is best absorbed. Molecular hydrogen is a separate topic entirely: hydrogen tablets dissolve hydrogen gas into water and do not change its mineral content.
How to read your own water in ten minutes
- Find your local water report. European utilities publish annual analyses per supply zone, usually with calcium, magnesium, sodium, chloride, sulfate, bicarbonate, hardness and conductivity.
- Look at calcium and magnesium first. Multiply by the litres you drink to see what water actually contributes to your intake.
- Check sodium and chloride. High values explain a salty or flat taste and are the profile tasting panels liked least.
- Compare your bottled water label to the same three numbers. The gap between brands is far larger than the marketing suggests.
- Match the treatment to the problem. Chlorine taste is a carbon filter question. Limescale is a hardness question. Neither is a reason to demineralise everything you drink.
Frequently Asked Questions
Is hard water bad for you?
There is no evidence that hard water is harmful at the levels found in normal drinking water supplies. If anything, the epidemiological literature points weakly in the other direction: a 2023 meta analysis found that higher total hardness was associated with lower cardiovascular mortality, while stressing high heterogeneity and the need for more research. Hard water is mainly an appliance and taste issue, not a health hazard.
Is soft water better?
Better for kettles and boilers, not automatically better for you. Softened water from an ion exchange unit has had its calcium and magnesium replaced by sodium, and very low mineral water is exactly the profile that tasting panels rated worst and that regulators worry about after desalination.
Does bottled mineral water contain more minerals than tap water?
Sometimes, and sometimes far less. European bottled waters were generally more mineral rich than North American tap water in one comparison, but across 21 countries the median calcium content of still bottled water differed by a factor of 18.7 between markets, and some popular brands contain under 10 mg/L calcium and around 2 mg/L magnesium. Read the label rather than the price.
Should I remineralise reverse osmosis water?
If reverse osmosis water is your main drinking water, it is reasonable to make sure the calcium and magnesium it no longer supplies come from elsewhere, whether from food, from a remineralisation cartridge or from a supplement. RO removes an estimated 92 to 99 percent of dissolved minerals, so it is a genuine gap in the mineral budget rather than a rounding error.
Does mineral content really change the taste that much?
Yes, and predictably enough that researchers could model overall liking from the chemistry alone. Both trained panellists and untrained volunteers preferred waters rich in calcium, bicarbonate and sulfate and disliked waters dominated by sodium, potassium and chloride.
Does the temperature or the bottle change anything?
Not chemically. Temperature and carbonation strongly affect perceived taste, and an insulated bottle keeps water at the temperature you actually enjoy drinking, but neither changes the mineral profile of what you poured in.
The Bottom Line
Water is not a neutral background to your diet. It carries a variable mineral load that shapes taste, scales your kettle and, depending entirely on where you live, contributes anywhere from almost nothing to a meaningful share of your daily calcium and magnesium. The evidence supports three modest, defensible statements: mineral content drives taste preference in a reproducible way, water can be a real source of well absorbed magnesium, especially when spread across the day, and very low mineral water gives you neither of those benefits. Everything beyond that, including the cardiovascular hardness literature, deserves interest rather than conviction. Look up your local analysis, read one bottle label properly, and you will know more about your water than almost anyone you meet.
Sources
- Azoulay A, Garzon P, Eisenberg MJ. Comparison of the mineral content of tap water and bottled waters. Journal of General Internal Medicine, 2001.
- Galan P et al. Contribution of mineral waters to dietary calcium and magnesium intake in a French adult population. Journal of the American Dietetic Association, 2002.
- Platikanov S et al. Influence of minerals on the taste of bottled and tap water: a chemometric approach. Water Research, 2013.
- Platikanov S et al. Predicting consumer preferences for mineral composition of bottled and tap water. Talanta, 2017.
- Sabatier M et al. Influence of the consumption pattern of magnesium from magnesium-rich mineral water on magnesium bioavailability. British Journal of Nutrition, 2011.
- Karagülle O et al. Magnesium absorption from mineral waters of different magnesium content in healthy subjects. Forschende Komplementärmedizin, 2006.
- Bykowska-Derda A et al. The Relationship between Mortality from Cardiovascular Diseases and Total Drinking Water Hardness: Systematic Review with Meta-Analysis. Foods, 2023.
- Kozisek F. Regulations for calcium, magnesium or hardness in drinking water in the European Union member states. Regulatory Toxicology and Pharmacology, 2020.
- Stoots SJM et al. Global Variations in the Mineral Content of Bottled Still and Sparkling Water. Journal of Clinical Medicine, 2021.
- Sengupta P. Potential health impacts of hard water. International Journal of Preventive Medicine, 2013.
- V K et al. The Role of Low Mineral Water Consumption in Reducing the Mineral Density of Bones and Teeth: A Narrative Review. Cureus, 2023.
- World Health Organization. Calcium and magnesium in drinking-water: public health significance, 2009.
- World Health Organization. Hardness in drinking-water: background document for development of WHO Guidelines for Drinking-water Quality.
This article is for general information and does not constitute medical advice. Food supplements are not a substitute for a varied and balanced diet and a healthy lifestyle.
