The World Health Organization has raised concerns about drinking demineralized water, including water produced by reverse osmosis (RO), because it strips out essential minerals like calcium and magnesium that your body relies on. The WHO commissioned a dedicated report, “Nutrients in Drinking Water,” specifically to examine the health consequences of long-term consumption of water produced through demineralization processes like reverse osmosis and desalination.
The core issue is straightforward: RO systems are extremely effective filters. They remove contaminants, but they also remove minerals your body absorbs from water every day. Over time, that absence can matter.
What the WHO Actually Found
The WHO convened experts to study what happens when people drink water that has been “manufactured” or “modified” to add or delete minerals. Their concern centered on water from demineralization processes, including reverse osmosis of fresh water and desalination of seawater or brackish water. The resulting report examined both the direct effects of low-mineral water on the body and the question of how to optimally reconstitute (remineralize) such water for health.
Epidemiological research from the US, Europe, and Russia cited in connection with these findings suggests health benefits are associated with drinking water containing at least 20 to 30 mg/L of calcium and 10 mg/L of magnesium. Most municipal tap water meets these thresholds. Reverse osmosis water typically falls far below them, often dropping to near-zero mineral content.
It’s worth noting that the WHO does not set a health-based guideline value for total dissolved solids (TDS) in drinking water. Their TDS ratings are based on taste: water below 300 mg/L tastes “excellent,” while water above 1,200 mg/L is considered unacceptable. RO water often measures below 50 mg/L, well below even the “excellent” taste range, which reflects just how thoroughly the process removes dissolved substances.
How Low-Mineral Water Affects Your Body
Drinking water with very low levels of sodium, potassium, magnesium, and calcium can disrupt the balance of fluids inside and outside your cells. This happens because your body constantly regulates the concentration of minerals in your blood and tissues. When you drink water that’s essentially mineral-free, it can alter the pressure balance across cell membranes, a condition researchers call osmotic stress. Your kidneys compensate by flushing out more minerals through urine, which can gradually deplete your reserves rather than replenish them.
Over time, this can contribute to low levels of key electrolytes. Research has identified several ways this matters. Magnesium deficiency is linked to muscle cramps, fatigue, and irregular heart rhythms. Calcium deficiency weakens bones. Low potassium affects nerve and muscle function. These aren’t theoretical risks: they’re well-established consequences of sustained mineral imbalances, and drinking demineralized water is one pathway that can contribute to them, particularly if your diet is also low in these minerals.
Cardiovascular and Long-Term Risks
The link between soft (low-mineral) water and heart disease has been studied for decades. An experimental study involving both animal models and young men found that consuming low-mineral purified water increased markers associated with cardiovascular disease risk compared to drinking mineralized water or tap water. This aligns with a broader body of epidemiological evidence showing that populations drinking harder, mineral-rich water tend to have lower rates of heart disease.
Some researchers have explored even more serious long-term concerns. A 2016 review published in Environmental Research examined how chronic electrolyte disturbances from demineralized water consumption could contribute to conditions at the cellular level, including DNA damage from sustained osmotic stress. The authors noted that disrupted electrolyte balance is among the most common features observed in cancer patients and discussed potential pathways through which prolonged mineral deficiency could promote harmful cellular changes. This research is preliminary in terms of establishing direct causation, but it highlights that the WHO’s concerns about demineralized water extend beyond simple nutrient gaps.
Cooking With RO Water Compounds the Problem
The concern isn’t limited to what you drink. When you cook vegetables, grains, or legumes in demineralized water, the water pulls minerals out of your food. Think of it like a sponge: water with no dissolved minerals has a stronger tendency to absorb them from whatever it contacts. This means that boiling potatoes or rice in RO water can leach calcium, magnesium, and other trace minerals into the cooking water, which typically gets poured down the drain. The net effect is that your meal delivers fewer minerals than it would if you’d cooked with tap water or mineralized water.
How to Add Minerals Back to RO Water
If you use a reverse osmosis system for its excellent contaminant removal but want to address the mineral issue, you have several practical options.
- Remineralization cartridge: Many newer RO systems include a built-in remineralization stage that adds calcium, magnesium, and potassium back into the filtered water. If your system doesn’t have one, add-on cartridges are available for most models. These typically need replacement every six months.
- Mineral drops: Concentrated liquid mineral supplements can be added to each glass of water. Dosage varies by brand, but it’s usually just a few drops per glass. This is a flexible option if you don’t want to modify your filtration hardware.
- Himalayan salt: A small pinch of unprocessed Himalayan salt per liter adds back a broad spectrum of trace minerals. It contains over 80 different minerals and trace elements, though the amounts of each are small.
- Alkaline pitchers: These use mineral balls or cartridges to raise pH and add minerals like calcium, magnesium, and potassium. However, they may not be sufficient to fully remineralize RO water, which starts at such a low mineral baseline.
The most reliable approach is a remineralization cartridge integrated into your RO system, since it treats all the water automatically rather than requiring you to dose each glass.
Putting the Risk in Context
Most of your daily mineral intake comes from food, not water. A balanced diet rich in leafy greens, nuts, dairy, and whole grains provides far more calcium and magnesium than even the most mineral-rich tap water. The WHO’s concern is most relevant for people who rely heavily on RO water, eat a diet that’s already low in minerals, or live in regions where demineralized water is the primary supply without remineralization infrastructure.
If you drink RO water occasionally or supplement with a varied diet, the risk is minimal. If RO water is your sole water source for drinking and cooking, remineralization is a simple step that addresses the WHO’s core concern without giving up the contaminant-removal benefits that make reverse osmosis appealing in the first place.