What decades of research tell us about magnesium, calcium and the water we drink every day.
We think carefully about what is in our food.
Protein. Fibre. Vitamins. Minerals. Salt. Sugar.
But when it comes to water, we tend to reduce everything to one question:
Am I drinking enough?
There is another question worth asking:
What is actually in the water I drink?
Because two glasses of perfectly clear water can look identical and have very different mineral compositions.
One may contain almost no magnesium or calcium. Another may contain meaningful amounts of both, together with bicarbonates and other dissolved minerals.
And over several decades, scientists have repeatedly asked whether those differences matter.
The answer is not simple. Water is not medicine, and epidemiological associations do not prove cause and effect.
But the accumulated evidence makes one thing increasingly difficult to dismiss:
drinking water is not nutritionally neutral.
Water can contribute meaningful amounts of minerals
Food remains our main source of magnesium and calcium.
But water can contribute too — sometimes substantially.
A Spanish study analysed tap water from 108 municipalities serving more than 21 million people, together with 109 bottled mineral waters.
The variation was enormous.
Among Spanish bottled waters, magnesium ranged from just 0.11 mg/L to 141.2 mg/L. The researchers calculated that water containing 15–45 mg/L magnesium could provide approximately 7.5–25.7% of recommended magnesium intake for adults, depending on water consumption.
They concluded that in parts of Spain, drinking water could represent an important supplementary source of magnesium.
That is an important concept.
A mineral does not necessarily have to provide your entire daily requirement to matter. A smaller amount, consumed consistently through the water you drink every day, contributes to total dietary intake.
And minerals in water are available to the body
The next question is obvious.
If magnesium is present in water, do we actually absorb it?
Human intervention studies suggest that we do.
In a double-blind, placebo-controlled study, 67 postmenopausal women consumed between 1.5 and 1.8 litres per day of either ordinary spring water or spring water supplemented with 120 mg/L magnesium and 650 mg/L bicarbonate for 84 days.
Serum magnesium increased significantly in the magnesium-bicarbonate group.
Importantly, the researchers did not find significant changes in blood pressure, serum lipids or most bone-metabolism markers during the study. Their more modest conclusion was nevertheless clear: regular consumption of magnesium-bicarbonate water provided a source of orally available magnesium.
This distinction matters.
There is solid reason to regard drinking water as a vehicle for mineral intake.
Whether that translates into specific long-term health outcomes is a more complicated scientific question.
The remarkable hard-water observation
That question has fascinated researchers since the 1950s.
Again and again, epidemiological studies noticed something unexpected:
communities drinking harder water often appeared to have lower rates of cardiovascular disease than communities drinking softer water.
Hardness is mainly created by dissolved calcium and magnesium.
The observation has now been investigated in many countries over several decades.
A systematic review and meta-analysis published in Foods in 2023 reviewed 25 studies examining drinking-water hardness and cardiovascular mortality.
Seventeen of those 25 reported a significant relationship between harder water and protection from cardiovascular mortality.
The quantitative analysis also found lower cardiovascular mortality in populations consuming harder water.
But there is an important qualification: heterogeneity between the studies was extremely high — I² = 96% — and eight of the 25 studies found either no relationship or a non-significant one.
The authors therefore concluded that water hardness could influence cardiovascular mortality, while emphasising that confounding factors make further research necessary.
That is probably the fairest way to describe the state of the science.
There is a persistent signal. It is not yet proof of causality.
Sardinia: geology, water and cardiovascular mortality
One particularly fascinating example comes from Sardinia.
Researchers analysed spring-water composition across all 377 municipalities on the island and compared it with 9,918 deaths from coronary artery disease between 1981 and 1991.
Municipalities supplied predominantly with softer water had an average standardized mortality ratio of 121.4, compared with 104.7 in harder-water municipalities — a statistically significant difference.
Higher calcium concentrations were significantly inversely associated with mortality from acute myocardial infarction and ischemic heart disease. Magnesium and bicarbonate showed similar inverse trends, although they did not reach conventional statistical significance.
The lowest coronary mortality was observed in areas where calcium- and bicarbonate-rich spring waters were traditionally consumed.
Again, this was an ecological study. It cannot tell us that mineral-rich water caused lower mortality.
Lifestyle, diet, genetics and many other variables matter.
But Sardinia illustrates why researchers continue to ask questions about the mineral composition of water rather than simply its purity.
Slovakia: more than 20,000 water analyses
Another unusually large investigation came from Slovakia.
Researchers combined 20,339 groundwater analyses, measuring 34 chemical parameters, with cardiovascular mortality data across 2,883 municipalities.
Among the water parameters studied, the strongest relationships with cardiovascular mortality were reported for the combined calcium-and-magnesium content, calcium and magnesium individually.
The researchers identified ranges associated in their model with the lowest relative cardiovascular mortality, including magnesium concentrations of approximately 42–78 mg/L.
This does not establish an “ideal” magnesium concentration for drinking water — the study was observational and geographically specific — but its scale makes the association difficult to ignore.
Hard water, younger arteries?
An even more unusual Slovak study looked not at mortality but at arterial stiffness.
Researchers examined 144 people living in areas supplied by waters with markedly different mineral compositions.
The soft-water group consumed water containing approximately:
20–25 mg/L calcium and 5–10 mg/L magnesium.
The harder-water group received approximately:
80–90 mg/L calcium and 25–30 mg/L magnesium.
People consuming the softer water showed greater arterial stiffness and a higher calculated arterial age.
The average difference between arterial age and actual age was almost five years greater in the soft-water population than in the harder-water population.
It was a relatively small observational study, so it should not be overinterpreted.
But it adds a different physiological endpoint to a literature dominated by mortality statistics.
What happens when researchers actually change the water?
Observational studies are interesting, but intervention studies are more informative because researchers deliberately change what people consume.
In a randomized, double-blind study of 70 people with borderline hypertension, participants drank either low-mineral water, magnesium-enriched water or natural mineral water for four weeks.
Among people who began the study with low urinary magnesium or calcium, consuming the magnesium-containing waters increased magnesium excretion — evidence that minerals delivered in the water affected mineral status.
The researchers also reported a significant reduction in blood pressure among participants consuming natural mineral water at two and four weeks. They specifically called for larger studies to investigate both mineral deficiency and the effectiveness of water as a vehicle for delivering magnesium and calcium.
Not every intervention has found such effects, which is why these findings should not become health claims.
But they reinforce the central point:
what is dissolved in the water can have measurable biological consequences.
Magnesium, water and metabolic health
The research extends beyond cardiovascular health.
A Serbian study compared healthy adults living in municipalities with very different magnesium concentrations in their drinking water.
One area had approximately 42 mg/L magnesium, while another had only 11 mg/L.
Diastolic blood pressure was lowest in the higher-magnesium area. Serum magnesium was also highest there, and after adjustment for age, gender and BMI, serum magnesium remained independently associated with several metabolic variables, including diastolic blood pressure and triglycerides.
Again: association, not proof.
But researchers have gone a step further with desalinated water.
A particularly interesting experiment with desalinated water
In 2022, researchers in Saudi Arabia conducted a randomized controlled trial in people with type 2 diabetes consuming desalinated drinking water.
The study is especially relevant because desalination removes almost all naturally occurring magnesium.
A total of 102 participants completed the trial. They received water containing either:
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0 mg/L added magnesium,
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20 mg/L, or
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50 mg/L magnesium.
After three months, the 50 mg/L group showed statistically significant improvements in HbA1c, insulin levels and HOMA-IR, a measure of insulin resistance.
Fasting glucose and lipid profiles, however, did not improve significantly.
The researchers themselves were cautious. The study was relatively small, had substantial dropout during the COVID period and needs confirmation.
But its design makes it noteworthy: rather than studying naturally occurring differences between populations, the researchers deliberately added magnesium back to desalinated water and measured the result.
Their paper also cites WHO guidance that when populations move from mineral-containing water to low-mineral desalinated supplies, consideration should be given to remineralisation with both calcium and magnesium.
Science also tells us to be cautious
It would be easy to select only positive studies.
That would give the wrong impression.
An ecological time-series study in England and Wales examined populations exposed to changes in drinking-water hardness between 1981 and 2005.
It found no evidence that changes in overall hardness or calcium altered cardiovascular mortality.
The researchers noted an important limitation: changes in magnesium concentrations were generally small, making it difficult to reach a definitive conclusion about magnesium specifically.
The 2023 systematic review reaches essentially the same broader conclusion.
A majority of studies point in one direction, but the results are heterogeneous and causality has not been established.
That is science doing its job.
The question is not settled.
But neither is it trivial.
The water world is changing
For most of human history, geology largely determined what was in our water.
Rain fell.
Water travelled through rocks and soil.
Minerals dissolved into it.
We drank the resulting water.
Today, technology increasingly intervenes in that journey.
Reverse osmosis, desalination, distillation and domestic purification systems can remove contaminants, salts — and essential minerals.
A review in the Journal of the American Water Works Association notes that conventional treatment generally leaves much of the calcium and magnesium intact, whereas softening can remove them and desalination can remove virtually all dissolved salts.
The same review concluded that drinking water can provide a consistent lifetime contribution to magnesium intake and summarized WHO discussions encouraging consideration of calcium and magnesium when demineralized waters are remineralized.
This creates a very modern question.
We have become extraordinarily good at deciding what should come out of water.
Perhaps we now need to think more carefully about what should remain — or be put back.
From hydration to mineral-balanced water
That question is at the heart of Aqvita.
We took our inspiration from natural mineral waters, where magnesium and calcium exist dissolved alongside bicarbonates and other minerals.
Instead of transporting those minerals together with litres of water in bottles, we asked whether the mineral component could be delivered separately.
Our approach is simple:
keep the water you already drink and add minerals to it.
Water becomes the format.
Not instead of a balanced diet.
Not as a medicine.
But as another way to integrate minerals into everyday life — through something we already consume repeatedly throughout the day.
The scientific literature does not tell us that there is one perfect water composition for everyone.
It does tell us something perhaps more fundamental:
all drinking water is not the same.
And after decades of thinking almost exclusively about how much water we drink, perhaps it is time to become more curious about what is in it.
Selected scientific references
Bykowska-Derda A, Spychala M, Czlapka-Matyasik M, et al. The Relationship between Mortality from Cardiovascular Diseases and Total Drinking Water Hardness: Systematic Review with Meta-Analysis. Foods. 2023;12:3255.
Dore MP, Parodi G, Portoghese M, Errigo A, Pes GM. Water Quality and Mortality from Coronary Artery Disease in Sardinia: A Geospatial Analysis. Nutrients. 2021;13:2858.
Rapant S, Fajčíková K, Cvečková V, et al. Chemical composition of groundwater and relative mortality for cardiovascular diseases in the Slovak Republic. Environmental Geochemistry and Health. 2015.
Rapant S, Cvečková V, Fajčíková K, et al. Hard Water, More Elastic Arteries: A Case Study from Krupina District, Slovakia. International Journal of Environmental Research and Public Health. 2019;16:1521.
Rylander R, Arnaud MJ. Mineral water intake reduces blood pressure among subjects with low urinary magnesium and calcium levels. BMC Public Health. 2004;4:56.
Day RO, Liauw W, Tozer LMR, et al. A double-blind, placebo-controlled study of the short-term effects of a spring water supplemented with magnesium bicarbonate. BMC Research Notes. 2010;3:180.
Rasic-Milutinovic Z, Perunicic-Pekovic G, Jovanovic D, et al. Association of blood pressure and metabolic syndrome components with magnesium levels in drinking water in some Serbian municipalities. Journal of Water and Health. 2012.
Maraver F, Vitoria I, Ferreira-Pêgo C, Armijo F, Salas-Salvadó J. Magnesium in tap and bottled mineral water in Spain and its contribution to nutritional recommendations. Nutrición Hospitalaria. 2015;31:2297–2312.
Albaker WI, Al-Hariri MT, Al Elq AH, et al. Beneficial effects of adding magnesium to desalinated drinking water on metabolic and insulin resistance parameters among patients with type 2 diabetes mellitus: a randomized controlled clinical trial. npj Clean Water. 2022;5:63.
Lake IR, Swift L, Catling LA, et al. Effect of water hardness on cardiovascular mortality: an ecological time series approach. Journal of Public Health. 2010;32:479–487.
This article is intended for general educational purposes. Associations reported in observational studies do not establish causality, and the evidence does not support using mineral water or food supplements to prevent or treat disease. Food supplements should not replace a varied, balanced diet and healthy lifestyle.