Magnesium dissolved in your tap water, well water, or bottled mineral water is not bad for you. In fact, the weight of evidence points in the opposite direction: populations drinking water with higher magnesium concentrations tend to have lower rates of heart disease, stroke, and possibly diabetes. The more interesting question is whether stripping magnesium out of water through softening or reverse osmosis might quietly work against your health. What follows is a look at what the research actually shows, where the benefits are strongest, and the handful of situations where the mineral content of your water genuinely matters.
Where the Magnesium in Your Water Comes From
Magnesium enters water naturally as it passes through rock and soil, dissolving out of minerals like dolomite and limestone. The concentration depends heavily on local geology. Some regions have “hard” water loaded with both calcium and magnesium, while others, particularly areas relying on desalinated seawater or surface water from granite catchments, have very little. Natural mineral waters from geologically rich areas can contain several tens of milligrams per liter of magnesium, and calcium concentrations can exceed 150 mg/L.1Journal of Energy and Safety Technology (JEST). Concentrations of Magnesium, Calcium and Potassium in Drinking Water; A Comparison between Tap Water and Bore Water Tap water and bore (well) water from the same region can differ, though in some studies the magnesium difference between the two is modest. What matters for health is not whether the water is “hard” in the laundry sense, but how much magnesium you actually absorb from it.
Your Body Absorbs Magnesium from Water Surprisingly Well
One common assumption is that the magnesium in water must be less useful to your body than the magnesium in food or supplements. A controlled study comparing magnesium absorption from mineral waters of different concentrations against bread and a supplement found no significant differences in 24-hour urinary magnesium excretion or in serum magnesium levels over a 10-hour window.2PubMed Central. Magnesium bioavailability from mineral waters with different mineralization levels in comparison to bread and a supplement In plain terms, your gut handles dissolved magnesium in water about as efficiently as it handles magnesium from solid food or a pill. This makes water a meaningful contributor to your daily magnesium intake, especially if you are already running low from your diet. Given that surveys consistently show a large share of adults fall short of the recommended daily magnesium intake, water is a delivery route worth paying attention to.
Heart Disease and Stroke Protection
The strongest evidence linking magnesium in drinking water to health benefits comes from cardiovascular research. A meta-analysis pooling data from multiple studies found that higher magnesium levels in drinking water were associated with about an 11% lower risk of coronary heart disease mortality.3PubMed Central. Magnesium Levels in Drinking Water and Coronary Heart Disease Mortality Risk: A Meta-Analysis The association was particularly strong in Scandinavian populations, which makes sense given that Nordic countries have some of the most detailed long-term water-quality records and population health registries.
Stroke risk follows a similar pattern. A large Taiwanese study found that people living in areas where drinking water contained at least 13.5 mg/L of magnesium had roughly 40% lower odds of dying from cerebrovascular disease compared to those in the lowest-magnesium areas.4PubMed. Calcium and magnesium in drinking water and risk of death from cerebrovascular disease A Swedish cohort study separated out the effects of calcium and magnesium individually and found that only magnesium, not calcium, remained independently associated with a reduced risk of ischemic stroke after adjustment, with the highest tertile of drinking water magnesium linked to about a 31% lower risk.5Oxford Academic (American Journal of Clinical Nutrition). Calcium and magnesium in drinking water and risk of myocardial infarction and stroke—a population-based cohort study
These are observational findings, so they cannot prove magnesium in water directly prevents heart attacks and strokes. People who live in areas with mineral-rich water may differ in other ways. But the pattern has shown up across enough countries and study designs to be taken seriously by researchers. Reviews of hard water and health have consistently flagged the association between water hardness and lower cardiovascular risk.6PubMed Central. Potential health impacts of hard water
Diabetes and Blood Sugar Control
The evidence connecting magnesium in water to diabetes is more mixed, but it leans positive. One ecological study found a significant protective effect of magnesium in drinking water on diabetes mortality.7PubMed. Magnesium in drinking water and the risk of death from diabetes mellitus A register-based study looking at type 2 diabetes incidence in young adults, however, did not find a clear-cut association, though suggestive findings appeared among young women.8PubMed. The regional association of rising type 2 diabetes incidence with magnesium in drinking water among young adults
The most concrete clinical evidence comes from a randomized trial in which patients with type 2 diabetes drank desalinated water enriched with 50 mg/L of magnesium daily for three months. Compared to the control group, these patients showed improved long-term blood sugar control (lower HbA1c), lower insulin levels, and reduced insulin resistance.9npj Clean Water. 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 Fasting blood glucose and lipid profiles did not budge, so the effect was specific to insulin sensitivity and glycemic control markers. The doses involved were modest, roughly what you would get from naturally mineral-rich tap water in many regions.
Bone Health and Hip Fracture Risk
Magnesium plays a role in bone mineralization, and some population-level data suggests that the mineral in drinking water may matter. A large Norwegian study found that people in municipalities with the highest concentrations of magnesium in their tap water had a meaningfully lower risk of hip fracture compared to those in the lowest-magnesium areas. The reduction was around 20% in men and 10% in women.10Elsevier / ScienceDirect (Bone). Nationwide data on municipal drinking water and hip fracture: Could calcium and magnesium be protective? A NOREPOS study Interestingly, calcium in the water did not show a consistent association with fracture risk in that study, so the protective signal appeared to come specifically from magnesium.
This finding aligns with broader concerns about what happens when you drink very low-mineral water for extended periods. A narrative review of the effects of reverse-osmosis-purified water noted that RO systems remove 92 to 99% of beneficial minerals including magnesium, and that long-term consumption of this demineralized water has been linked to bone and tooth demineralization.11PubMed Central. The Role of Low Mineral Water Consumption in Reducing the Mineral Density of Bones and Teeth: A Narrative Review The review raised the point that very low-mineral water may actually draw minerals from the body and increase their excretion through urine. For people who rely entirely on RO-filtered water at home without remineralization, this is worth knowing about.
The Calcium-to-Magnesium Ratio
It is not just the amount of magnesium in your water that matters. The ratio of calcium to magnesium appears to influence certain health outcomes. An experimental study looking at kidney stone formation found that remineralizing purified water with calcium-to-magnesium ratios of 0.5 and 3.4 significantly reduced calcium oxalate crystal formation and renal injury, while extreme ratios above 10 offered no benefit.12PubMed Central. Impact of Calcium–Magnesium Ratio in Purified Water Remineralization on Calcium Oxalate Crystal Formation and Renal Injury If you drink water that is very high in calcium but very low in magnesium, the imbalance may partially offset the benefits of either mineral alone.
This has practical implications for anyone choosing a home water treatment system. Softeners and RO systems that strip out everything and then add back only calcium, or no minerals at all, may create an unfavorable ratio. If you remineralize, getting a reasonable balance of both minerals seems to be what the evidence supports.
Pregnancy and Maternal Health
Magnesium in drinking water has been specifically studied in pregnancy, and the results are worth flagging. A study examining preeclampsia rates across different neighborhoods of a city found that the occurrence of this dangerous pregnancy complication varied inversely with the magnesium content of local drinking water. Areas with more magnesium in the water had lower preeclampsia rates.13PubMed. Influence of the magnesium content of drinking water and of magnesium therapy on the occurrence of preeclampsia A separate study found a similar trend for very low birth weight deliveries: higher magnesium in drinking water was associated with a decreased risk of delivering a very low birth weight infant.14Magnesium Research. Magnesium in drinking water and the risk of delivering a child of very low birth weight
These are observational findings, and neither study can fully separate the effect of water magnesium from other neighborhood-level differences. But given that magnesium supplementation is already used clinically to manage preeclampsia and preterm labor, the idea that baseline intake through water could play a supporting role is biologically plausible. Pregnant women in areas with very soft or desalinated water may want to discuss mineral supplementation with their providers.
What Happens When You Remove Magnesium from Water
The flip side of the benefits question is what happens when magnesium is deliberately stripped out. This is not hypothetical. Millions of households use water softeners, reverse osmosis systems, or receive desalinated water. RO systems remove the vast majority of dissolved minerals, and conventional ion-exchange softeners swap calcium and magnesium for sodium.
Scale buildup from calcium and magnesium carbonate is a genuine household headache. It clogs pipes, reduces water heater efficiency, and leaves residue on fixtures. Research has documented that elevated hardness and alkalinity in water accelerate scale formation in distribution systems, and softening technologies are widely deployed to address it.15Elsevier. Control approach and evaluation framework of scaling in drinking water distribution systems: A review However, those same softening technologies alter fundamental water quality characteristics, including mineral content that your body may need.
A study looking at the shift to desalinated water in an Israeli population found that adoption of desalinated water was associated with a significant decrease in serum magnesium concentrations. The researchers looked for a corresponding increase in dementia prevalence and did not find a clear one, though they cautioned that a small effect could not be ruled out.16PubMed. Water desalination, serum magnesium and dementia: a population-based study The serum magnesium finding itself is telling: switching your main water source to one stripped of minerals can shift your body’s magnesium status, even if the downstream health effects take years to manifest.
If you use an RO system at home, adding a remineralization filter is a simple fix. Some bottled mineral waters naturally contain magnesium at levels comparable to what hard tap water provides, which is another option if your local supply is mineral-poor. The goal is not to chase a specific number but to avoid drinking completely demineralized water as your sole hydration source day after day.
Exercise, Cramping, and Magnesium-Rich Hydration
Athletes lose magnesium through sweat, and magnesium-enriched hydration has been tested as a way to reduce exercise-associated muscle cramps. A study of half-marathon runners compared those who hydrated with a magnesium-rich electrolyte mix against those who drank plain water. Roughly 46% of the water-only group experienced muscle cramps, compared to about 21% in the magnesium group. The reduction held for both mild and severe cramps.17Journal of Exercise and Nutrition. A Magnesium-Rich Electrolyte Hydration Mix Reduces Exercise Associated Muscle Cramps in Half-Marathon Runners This was a specific electrolyte product rather than ordinary tap water, so the doses were higher than what you would get from a glass of mineral-rich water. Still, the finding reinforces the broader point that magnesium status matters for muscle function, and that water can be part of the delivery system.
When Magnesium in Water Could Actually Cause Problems
At the concentrations typically found in drinking water, magnesium is not harmful for healthy adults. The amounts involved, usually somewhere between 1 and 100+ mg/L depending on geography, are well within safe bounds. The tolerable upper intake level set by health authorities applies to supplemental magnesium (from pills and fortified products), not to magnesium naturally present in food and water.
Very high magnesium levels can cause loose stools. This is the same mechanism that makes magnesium citrate an effective laxative. But this effect generally requires much higher doses than what drinking water delivers. If your water is extremely mineral-rich and you are prone to digestive sensitivity, you might notice softer stools, but this is unlikely to be a health concern.
The more relevant caution involves drug interactions. Magnesium can interfere with the absorption of certain medications, particularly some antibiotics. Tetracycline antibiotics, for example, bind to magnesium, calcium, and zinc in the gut, which reduces how much of the drug gets into your bloodstream.18PubMed Central. Magnesium and Drugs Conversely, some drugs can increase magnesium loss. Certain diuretics, for instance, promote magnesium excretion through the kidneys. If you take medications that interact with minerals, the magnesium content of your water probably is not the main variable to worry about (supplements and antacids deliver much higher doses), but it is worth being aware of if your doctor has flagged mineral interactions as an issue for you.
People on Kidney-Related Restrictions
People with significantly impaired kidney function sometimes need to limit magnesium intake because their kidneys cannot excrete it efficiently. In healthy kidneys, excess magnesium is filtered out without issue. When kidney function drops below a certain threshold, magnesium can accumulate in the blood, a condition that in severe cases leads to muscle weakness, low blood pressure, and cardiac problems. If you have advanced chronic kidney disease and your nephrologist has given you mineral restrictions, magnesium in water is something to factor in. For everyone else, the kidneys handle the amounts in drinking water without breaking a sweat.
Hard Water Taste and the Household Trade-Off
The reason many people soften their water has nothing to do with health. Hard water tastes different, leaves scale on kettles and showerheads, makes soap lather poorly, and shortens the life of water heaters and appliances. These are real quality-of-life annoyances. The trade-off is that softening removes minerals your body can use. One practical middle ground is to soften the hot water lines and appliance feeds while leaving the cold kitchen tap unsoftened, so you still get mineral-rich water for drinking and cooking. Another approach is to use a whole-house softener but install a small remineralization or bypass system for the drinking water tap. Neither solution is exotic or expensive, but it does require thinking about the plumbing setup rather than just installing a single system and forgetting about it.
Taste preferences vary. Some people prefer the cleaner, more neutral taste of soft or RO-treated water. If that is you, and you compensate by eating a magnesium-rich diet (leafy greens, nuts, seeds, legumes), you are probably fine. The concern is mostly about people who drink demineralized water, eat a diet already low in magnesium, and do not supplement. That combination can leave you chronically short of a mineral involved in hundreds of enzymatic processes in the body.