Yes, reverse osmosis removes the vast majority of dissolved minerals from water, typically 90 to 99 percent, including calcium and magnesium. For most people this isn’t a health risk, because food supplies the bulk of daily mineral intake, not water. But the World Health Organization has flagged low-mineral water as worth a second look, especially for people who drink a lot of it and get little calcium or magnesium elsewhere. The practical fix, remineralization filtration, is simple, cheap, and already built into most modern RO systems.
That’s the short version. Here’s the longer one, because “does RO water matter to your health” isn’t a yes-or-no question, it’s a “how much, and for whom” question.
How Much Does Reverse Osmosis Actually Remove?
RO membranes reject 90 to 99 percent of dissolved solids, and mineral-specific studies put calcium removal around 97 percent and magnesium removal around 96 percent. A tap water sample running 300 ppm total dissolved solids (TDS) typically comes out the other side of an RO membrane at 15 to 30 ppm.
That’s the whole point of the technology. RO membranes were engineered to reject dissolved salts, metals, and organic compounds indiscriminately, because the process doesn’t distinguish between a contaminant and a mineral your body might want. Both are dissolved solids to a semipermeable membrane. So yes, if you’re drinking straight RO output with no additional treatment, you’re drinking water with very little calcium, magnesium, potassium, or bicarbonate left in it.
Is Water a Meaningful Source of Minerals in the First Place?
For most people, no, not a large one. Research reviewed by the World Health Organization found that drinking water typically supplies less than 5 to 10 percent of daily magnesium intake, with the rest coming from food. Calcium’s contribution from water varies more depending on local mineral content, generally landing in the range of low single digits up to around 10 to 15 percent of total dietary calcium in harder water regions, and dairy alone can cover more than half of most people’s calcium intake on its own.
So water is a secondary source for most of the population, not the primary one. That’s the context that gets lost in a lot of alarmist content about RO water: for someone eating a normal, varied diet, losing water’s small mineral contribution isn’t going to create a deficiency by itself.
Then Why Does WHO Flag Demineralized Water as a Concern?
Because “most people” isn’t “everyone,” and because the research on low-mineral water isn’t purely about nutrition, it’s also about how the water behaves once it’s inside the body and inside your plumbing.
WHO’s technical review on demineralized drinking water noted a few specific findings worth taking seriously:
– Populations drinking water low in calcium and magnesium showed higher rates of cardiovascular mortality in some epidemiological studies compared to populations drinking harder, more mineralized water.
– Low-mineral water intake has been associated with a higher fracture risk in children and lower bone density in some adult studies.
– WHO’s working guidance suggests a practical minimum of 150 to 300 mg/L total dissolved solids in drinking water, with calcium around 20 mg/L and magnesium around 10 mg/L, as a reasonable target rather than a hard regulatory limit.
It’s worth being precise about what this evidence does and doesn’t say. WHO has been explicit that there isn’t enough long-term controlled data to issue a blanket warning against demineralized water, and it hasn’t set an enforceable global standard. What it has said is that remineralization is a “prudent precaution,” particularly for people who drink large volumes of very low-TDS water as their main fluid source, and particularly relevant in regions where desalination or heavy purification is the primary water supply, not just a home filter.
There’s also a taste and equipment angle that’s less dramatic but very real: water stripped of essentially all minerals tends to taste flat, and very low-TDS water is mildly more corrosive to plumbing and appliances over time because it’s chemically “hungry” for dissolved solids.
Who Should Actually Care About This?
The people for whom remineralization matters most are the ones drinking large volumes of straight RO or distilled water as their near-total fluid intake, day after day, for years, especially if their diet is also lower in dairy, leafy greens, and other mineral-dense foods. That includes some households on whole-house RO systems, some regions relying on desalinated water, and people using RO as their only water source without any other filtration step.
For the average household running a standard under-sink or whole-house RO system alongside a normal diet, the mineral loss from the water itself is a minor factor. It’s not nothing, it’s just not the headline health risk some scraped content and forum threads make it out to be. The more consistently useful reasons to remineralize are taste, pH balance, and reduced corrosivity, with the mineral contribution as a genuine but secondary benefit.
How Does Remineralization Filtration Actually Fix This?
A remineralization or alkaline cartridge installs after the RO membrane, as the last stage before the water reaches the faucet, and it reintroduces minerals as the water passes through.
Most cartridges use calcite (calcium carbonate) or a calcite and magnesium oxide blend. As water flows through the media, small amounts dissolve back into it, which does two things at once: it raises pH from RO water’s typically slightly acidic 5 to 6 range back toward neutral or mildly alkaline, usually a rise of about 1 to 2 pH points, and it adds back measurable calcium and magnesium, generally enough to bring TDS up moderately without re-introducing the higher mineral loads (and associated hardness or scale) of untreated tap water.
The result is water that keeps RO’s contaminant rejection, which is the actual point of the system, while addressing the flat taste, low pH, and mineral-stripping side effects of straight RO output. It’s a well-understood, inexpensive addition, not a redesign of the filtration process.
This is the layer AMPAC USA builds into its residential reverse osmosis systems and commercial reverse osmosis water purification equipment: RO for contaminant removal, paired with remineralization stages so the output isn’t just clean, it’s also water people actually want to drink and that won’t slowly eat away at pipes and fixtures. If you’re evaluating reverse osmosis for a home or facility, remineralization is worth specifying up front rather than adding later, since it’s far easier to build into the initial system than to retrofit.
What About Alkaline Water Specifically, Is That the Same Thing?
Related, but not identical. Alkaline water refers to water with a higher pH, generally above 8, achieved either through added minerals (the same calcite/magnesium oxide approach used in remineralization) or through electrolysis in dedicated alkaline water ionizers. Remineralization filters raise pH as a byproduct of adding minerals back to RO water. Standalone alkaline systems are built specifically to push pH higher, sometimes independent of an RO stage at all.
The health claims around alkaline water specifically (beyond the mineral content question) are a separate and more contested topic, mostly built on smaller or preliminary studies rather than the kind of population-level data WHO has reviewed for mineral content. What’s well established is narrower and more useful: a remineralized RO system produces water that’s closer to neutral pH, tastes better, and retains a modest, useful mineral content, without needing to lean on the more speculative claims sometimes attached to alkaline water marketing.
The Bottom Line
Reverse osmosis does remove most minerals from water, that part isn’t in dispute. Whether it matters depends on how much of that water you drink, what the rest of your diet looks like, and whether the system has a remineralization stage. For most households, it’s a manageable, well-solved problem, not a reason to avoid RO filtration, which still does the more important job of removing contaminants that don’t belong in drinking water in the first place.
Frequently Asked Questions
Does reverse osmosis remove all minerals from water?
No, but it removes most of them, typically 90 to 99 percent of total dissolved solids, including roughly 96 to 97 percent of calcium and magnesium. A small amount of residual mineral content usually remains, but it’s low enough that taste and pH are noticeably affected without a remineralization stage.
Is it unhealthy to drink RO water without remineralization?
For most people eating a typical varied diet, no, since food supplies the large majority of daily calcium and magnesium intake. WHO research has flagged potential concerns, mainly cardiovascular and bone-density associations in populations drinking large volumes of low-mineral water long-term, which is why remineralization is recommended as a precaution rather than treated as optional.
How do I know if my RO system has remineralization built in?
Check the filter stage list from the manufacturer. A remineralization or alkaline cartridge is usually listed as the final stage before the faucet, often labeled as a “calcite,” “alkaline,” or “mineral” filter. If your system only lists sediment, carbon, and RO membrane stages, it likely isn’t remineralizing the output.
Does remineralized RO water taste different from regular tap water?
Yes, generally better to most people. Straight RO water often tastes flat because it lacks dissolved minerals. Remineralization adds a modest, controlled amount of calcium and magnesium back in, which restores a rounder taste without reintroducing the higher hardness levels of untreated tap water.
Is alkaline water the same as remineralized water?
Not exactly. Remineralization adds minerals back to RO water, which also raises pH slightly. Standalone alkaline water systems are built specifically to raise pH higher, sometimes via electrolysis rather than added minerals, and the additional health claims around alkaline water beyond mineral content are less well established than the WHO research on mineral content itself.
Sources: World Health Organization, Health Risks from Drinking Demineralised Water (Rolling Revision of the WHO Guidelines for Drinking-Water Quality); WHO, Calcium and Magnesium in Drinking-Water: Public Health Significance; Epidemiology, Daily Intake of Magnesium and Calcium From Drinking Water; ScienceDirect, Contribution of Mineral Waters to Dietary Calcium and Magnesium Intake.
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