Mineral Water, Drinking Water and Hard Water: How Much Calcium, Magnesium and Sodium Do They Provide?
How much calcium, magnesium and sodium tap, bottled mineral and hard water provide, what WHO and studies say, and when water softeners or filters change the minerals.
Content last updated . This page has not been medically reviewed.
Quick answer
Drinking water can supply some calcium and magnesium, and sometimes sodium, but the amount varies enormously from one source to another. For most waters in the studies we read, the share of daily needs was small. WHO says drinking-water may be a contributor of calcium and magnesium and could matter for people who are marginal for these minerals. [1]
Labels used: absorption study means a trial measuring how much mineral is absorbed; mixed means sources disagree; Proper evidence not found means we searched and found nothing usable.
Terms
- Hardness is mostly calcium and magnesium dissolved in water, usually expressed as milligrams of calcium carbonate per litre. WHO classes below 60 mg/L as soft, 60 to 120 as moderately hard, 120 to 180 as hard, and above 180 as very hard. [1]
- Packaged water can be spring water, mineral water or bottled tap water; WHO notes total dissolved solids range from almost zero to several thousand mg per litre. [1]
- Demineralized water has had minerals removed. WHO says desalination by nanofiltration, reverse osmosis or thermal methods depletes the mineral content. [1]
What measurements show
| Source | Finding | Country and year |
|---|---|---|
| 92 bottled waters bought in Indianapolis | Calcium ranged from under 0.1 to 360 ppm (median 5.2); magnesium from under 0.01 to 106 ppm (median 1.9); sodium up to 109 ppm (median 2.9). Most waters did not provide meaningful shares of calcium or magnesium RDAs, though some did [2] | US, 2020 |
| Direct-drinking water in primary schools, Taicang | Water contributed about 8.95% of children's dietary calcium intake and 2.78% of magnesium intake (2.63% and 1.96% of the recommended nutrient intake); nanofiltration and reverse osmosis cut calcium and magnesium sharply [3] | China, 2024 |
| 40 natural mineral waters on the Polish market | Sodium and potassium varied widely; one litre supplies no more than several percent of the recommended daily potassium intake [4] | Poland, 2016 |
WHO also notes calcium and magnesium contributions from drinking-water vary greatly with the mineral content of the source water. [5]
Does mineral water help?
- Calcium absorption. A meta-analysis of four small studies found calcium absorption from calcium-rich mineral water was at least comparable to, and possibly better than, absorption from dairy products. [6] A 2023 systematic review described calcium-rich mineral waters as promising but said more research was needed. [7] This is an absorption measure, not a fracture or bone outcome.
- Heart health and hardness. WHO (2011) says some epidemiological studies suggest a protective effect of magnesium or hardness on cardiovascular mortality, but that the evidence is debated and does not prove cause. It found insufficient data to propose minimum or maximum concentrations of minerals in water. [1] Evidence is mixed and not established.
- Growth in children. A retrospective cohort in Chinese primary schools found no difference in height growth between children drinking water with normal calcium and magnesium and those drinking low-mineral water. [3] It is observational and from one city.
Sodium, softeners and taste
WHO gives an average taste threshold for sodium in water of about 200 mg per litre and has set no health-based guideline, as the contribution from drinking-water to daily intake is small. [8] Water softeners that exchange ions replace each calcium or magnesium ion with two sodium ions, raising sodium and chloride and lowering the calcium and magnesium you drink. [1] If you follow a sodium-restricted diet, ask your clinician whether a softener or a mineral water matters for you. See Sodium and Chloride.Fluoride in bottled water
The US bottled-water study found fluoride in 90 of 92 waters too low to help prevent cavities. [2] See Mineral Supplements and Child Safety Beyond Iron for fluoride cautions in children.Frequently asked questions
Is hard water good for you?
WHO says evidence about hardness and cardiovascular risk is debated and does not prove cause, and it proposes no guideline value for minerals in water. [1]
How much calcium and magnesium is in tap water?
It varies widely with the source. [5] Check your local water quality report.
Is bottled mineral water better than tap water?
Mineral content varies from almost nothing to several thousand mg per litre of total dissolved solids. [1] Neither type is better in general; read the composition.
Does a water softener remove minerals?
It replaces calcium and magnesium with sodium, so sodium goes up. [1]
Does reverse osmosis water lack minerals?
Yes, in the school study calcium and magnesium were much lower in water from nanofiltration and reverse-osmosis systems. [3]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Safety and who should ask first
Waters high in minerals can add magnesium, potassium or sodium. People with kidney disease, heart or blood pressure conditions, or on sodium or potassium limits should ask a clinician before drinking mineral waters regularly. See Minerals, Supplements and Kidney Disease. WHO says the public should have access to information on the mineral composition of bottled or packaged water. [1] Check labels and your local water utility report. Mineral-water amounts do not replace a clinician's advice about calcium for bones; see Calcium and Osteoporosis and Bone Health.
References
- World Health Organization. Hardness in Drinking-water: Background document for development of WHO Guidelines for Drinking-water Quality (WHO/HSE/WSH/10.01/10/Rev/1), 2011. Read 2026-10-23.
- Almejrad L, et al. An investigation into the potential anticaries benefits and contributions to mineral intake of bottled water. J Am Dent Assoc 2020;151(12):924-934. Read 2026-10-23.
- Gu H, et al. Contribution of direct-drinking water to calcium and magnesium and the influence on the height in school-age children. Front Nutr 2024;11:1434952. Read 2026-10-23.
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- Cotruvo J, Bartram J, eds; World Health Organization. Calcium and Magnesium in Drinking-water: Public health significance, 2009. Read 2026-10-23.
- Böhmer H, et al. Calcium supplementation with calcium-rich mineral waters: a systematic review and meta-analysis of its bioavailability. Osteoporos Int 2000;11(11):938-943. Read 2026-10-23.
- Pop MS, et al. Exploring the Potential Benefits of Natural Calcium-Rich Mineral Waters for Health and Wellness: A Systematic Review. Nutrients 2023;15(14):3126. Read 2026-10-23.
- World Health Organization. Guidelines for Drinking-water Quality, 4th edition: Chapter 10, Acceptability aspects: taste, odour and appearance. Read 2026-10-23.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.