Is Purified Water Safe to Drink? Benefits and Risks

Purified water is safe to drink in the short term and effectively removes many harmful contaminants, but relying on it as your sole water source over months or years raises concerns that most people never consider. The purification process strips out not just pollutants but also naturally occurring minerals like calcium, magnesium, and fluoride, and a growing body of research links long-term consumption of very low-mineral water to subtle health effects, particularly in children. The safety picture depends on how the water is purified, what you eat alongside it, and how long you depend on it.

What Purification Strips Out

The term “purified water” covers several technologies, but the most common in consumer products and home systems are reverse osmosis (RO), nanofiltration, and distillation. All of them are remarkably good at removing things you do not want. RO membranes reject more than 85% of most pharmaceutical compounds found in source water, and nanofiltration performs similarly for the majority of tested drugs.¹ For newer pollutants like per- and polyfluoroalkyl substances (PFAS), which have attracted public alarm in recent years, RO membranes also show effective removal, with rejection rates increasing for larger PFAS molecules.²

The catch is that these membranes do not distinguish between harmful contaminants and beneficial dissolved minerals. RO systems remove an estimated 92–99% of minerals like calcium, magnesium, and fluoride.³ Distillation does the same by evaporating water and leaving dissolved solids behind. The result is water that is chemically very pure but also very empty. Whether that emptiness matters depends on what else you eat and drink, and how long purified water is your primary source.

The Cardiovascular Case for Minerals in Water

The most studied health question around low-mineral water involves the heart and blood vessels. Researchers have been investigating the relationship between water hardness (a measure of dissolved calcium and magnesium) and cardiovascular disease for decades, and the pattern that keeps emerging centers on magnesium. A large review of epidemiological studies found that many ecological studies reported a protective association between water hardness and cardiovascular mortality, with the strongest and most consistent signal tied to magnesium rather than calcium.⁴

A Taiwanese study examining cerebrovascular disease deaths reinforced this pattern. People whose drinking water contained higher magnesium levels had substantially lower odds of dying from stroke, with the highest-magnesium group showing roughly 40% lower odds compared to the lowest group. Calcium levels, once magnesium was accounted for, did not independently affect risk.⁵ More recent data from over 324,000 UK Biobank participants found that each increase in water magnesium was associated with a small but measurable decrease in overall cardiovascular disease risk.⁶

The evidence is not ironclad. The same review that found a consistent magnesium signal noted that analytical studies (which control for confounders better than ecological ones) provide little evidence that water hardness or calcium levels independently affect cardiovascular risk.⁴ In other words, the magnesium link looks real but modest, and the calcium link is weaker than many health websites suggest. If you eat a diet rich in leafy greens, nuts, seeds, and legumes, you are probably getting enough magnesium regardless of what water you drink. But if your diet is marginal, losing the magnesium contribution from water could matter.

Teeth, Bones, and Fluoride

Fluoride occupies a unique position in the purified-water debate because many public water systems add it specifically to prevent tooth decay. RO and distillation remove fluoride just as efficiently as they remove other dissolved substances. A narrative review examining this issue concluded that the combined effect of consuming low-mineral water, with its reduced calcium, magnesium, and fluoride, has been linked to demineralization of bones and teeth, raising the risk of both osteoporosis and dental cavities.³

A study of Chinese schoolchildren gave the concern a concrete face. Schools using low-mineral direct drinking water (DDW) systems saw higher rates of dental cavities among students compared to schools with normal mineral-content water. The exposure was also flagged as a risk factor for reduced height growth, with the risk ratio for dental caries reaching about 1.8 for children drinking low-mineral water.⁷ The researchers concluded that schools should choose water treatment systems that retain minerals.

For adults who brush with fluoride toothpaste and see a dentist regularly, losing waterborne fluoride is likely a minor issue. For children whose teeth are still developing, and for communities where fluoridated water is the primary source of fluoride exposure, switching to purified water without supplementation is a more consequential decision.

Effects on Children

Children appear more sensitive to the mineral profile of their drinking water, partly because they drink more water relative to their body weight and partly because their bodies are actively building bone and other tissues. The Chinese school study noted above found effects on both dental health and growth. A separate study tracked children who drank very low-mineral DDW over four years and found they had significantly higher levels of homocysteine, a marker associated with cardiovascular risk, along with lower levels of vitamin B6, vitamin B12, and other nutrients compared to children drinking normal water.⁸ The researchers flagged elevated homocysteine as an early warning sign for cardiovascular problems later in life.

A large Taiwanese study of over 146,000 children examined whether drinking purified versus tap water during infancy affected gut health. Children in the purified water group had a slightly higher risk of developing irritable bowel syndrome, with a hazard ratio of about 1.05 after adjusting for confounders.⁹ A 5% increase in risk is small, and this is a single observational study with limitations, but it raises the possibility that the mineral or microbial profile of early drinking water influences gut development in ways we do not fully understand yet.

None of this means purified water is dangerous for children in the way that contaminated water is. But if your household relies exclusively on RO water, especially for formula preparation and early childhood drinking, it is worth thinking about whether minerals are being replaced through food or supplements.

Does Your Body Absorb Purified Water Differently?

A persistent claim in wellness circles is that purified or distilled water “leaches minerals from your body.” The reality is more mundane. Your intestines absorb water regardless of its mineral content. A study directly measuring intestinal fluid absorption found that the gut absorbed distilled water efficiently, at a rate of about 9.4 milliliters per hour per centimeter of intestine.¹⁰ The concern is not that purified water pulls minerals out of your tissues on contact. It is that by drinking mineral-free water instead of mineral-containing water, you miss out on a dietary source of minerals you would otherwise get passively. Over time, in someone with a poor diet, those missing contributions add up.

How your kidneys handle the water is another piece of the picture. When you drink very low-electrolyte fluids, the body adjusts hormone levels to manage sodium and other electrolytes. A crossover study in fasting adults found that fluid composition affected aldosterone (a hormone that regulates sodium retention) and urine electrolyte concentrations.¹¹ In everyday life, this is not a problem because you eat food alongside your water, and food provides the electrolytes your kidneys need to maintain balance. In edge-case scenarios, such as extreme fasting, prolonged exercise with only distilled water, or exclusive reliance on purified water without food, electrolyte dilution becomes a genuine risk.

Microbial Concerns With RO Systems

People buy RO systems partly for microbial safety, and the membranes do filter out bacteria and viruses from the incoming water. But the treated side of an RO system is not a sterile environment. Research has consistently found that bacteria recolonize the permeate side of RO membranes, and the species that thrive there are often different from those in the incoming water. A study of a drinking water RO plant found that bacterial growth persisted after treatment, with isolates showing the capacity to form biofilms and resistance to several antibiotics.¹²

Biofilm formation on RO membranes is recognized as one of the system’s most serious operational problems. The biofilm not only degrades membrane performance over time but can harbor opportunistic pathogens and antibiotic-resistant bacteria.¹³ For commercial and municipal systems, this is managed through regular membrane replacement and disinfection. For home systems, the risk depends entirely on maintenance. A neglected under-sink RO unit with old filters and a standing-water tank can become a microbial breeding ground, potentially delivering water that is worse than the tap supply it was meant to improve.

The practical takeaway: if you use a home RO system, replace filters and membranes on the manufacturer’s schedule, drain and clean the storage tank periodically, and do not assume the output is automatically safer than your municipal tap water.

How Purification Changes Taste

Purified water tastes different from tap or mineral water, and the difference is not imaginary. Dissolved minerals directly affect how water tastes. Sensory research using trained panelists found that four out of six analyzed mineral nutrients had a measurable impact on the perceived taste of water.¹⁴ A separate chemometric study found that panelists preferred water with moderate total dissolved solids and relatively high concentrations of bicarbonate, sulfate, calcium, and magnesium, while high sodium, potassium, and chloride levels were scored poorly.¹⁵

Strip all those minerals out through RO or distillation and you get water that many people describe as “flat” or “empty.” Some find it unpleasant enough that they drink less of it, which is its own health issue. Others prefer the neutrality. The taste question matters for a practical reason beyond preference: purified water that sits in contact with the atmosphere absorbs carbon dioxide, forming a mild carbonic acid that lowers the pH slightly. Research has confirmed that CO₂ dissolving into water reduces its pH.¹⁶ The resulting mildly acidic taste is not harmful, but it can make the water taste slightly sour, which contributes to the perception that “something is off.”

Cooking With Purified Water

If your household runs on purified water, it is also the water you boil pasta in, cook rice with, and steep tea in. There is an often-overlooked interaction here. When you boil vegetables in purified (very low-mineral) water, minerals leach out of the food and into the cooking water more aggressively than they would in harder water, because of the steeper concentration gradient between the food and the surrounding liquid. Research on potatoes found that boiling cubed tubers reduced potassium levels by about 50%, with similar reductions in phosphorus, magnesium, and several trace minerals.¹⁷ If you discard the cooking water, those minerals go down the drain.

For most people eating varied diets in developed countries, this mineral loss during cooking is marginal. But for someone already on the edge nutritionally, relying on purified water for both drinking and cooking can compound the deficit. Steaming rather than boiling preserves more minerals in the food, and using cooking liquid in sauces or soups rather than discarding it captures what leaches out.

What About the Container?

Purified water sold commercially arrives in plastic bottles, and purified water has a quirk that makes container chemistry slightly more relevant. Because it has very few dissolved solids, it is more chemically “hungry” than mineralized water, meaning it has a marginally greater tendency to pick up trace substances from whatever it touches. Research found that the leaching of certain elements like antimony, lead, and barium from bottles depended partly on water quality (how much was already dissolved in it) and partly on the container material itself.¹⁸ The same study detected BPA in samples from polycarbonate containers but not from other types.

A study that specifically assessed the safety of reusing PET bottles (the most common plastic for bottled water) found that plasticizer concentrations were well within safe limits, with a minimum safety factor of 8.5 for the more concerning compound tested. The researchers concluded that PET bottles did not pose a meaningful health risk from plasticizer migration, even under sun exposure and heat.¹⁹ The main variable that mattered was the country of origin of the bottles, not storage conditions. So while the “purified water leaches chemicals from plastic” fear is overblown for standard PET bottles used under normal conditions, storing any water, especially low-mineral water, in old polycarbonate containers for long periods at high temperatures is worth avoiding.

Remineralization and Practical Fixes

If you like the taste and contaminant-removal benefits of purified water but want to offset the mineral loss, the solution is straightforward: add minerals back. Many commercial water purification systems now include a remineralization stage, typically a cartridge containing calcium and magnesium salts that dissolves small amounts back into the treated water. Mineral drops and tablets sold for this purpose are widely available. Even adding a pinch of unrefined sea salt or a squeeze of lemon to a glass of RO water introduces some trace minerals and improves the taste for most people.

Alternatively, mineral-rich foods fill the gap without changing your water source. A handful of almonds delivers more magnesium than several liters of even relatively hard tap water. A glass of milk provides more calcium than a day’s worth of mineral-containing water. The minerals in water matter most for populations that have limited access to diverse foods or are in developmental stages where every milligram counts, which is why the concern is most pressing for children in institutional settings (like the schools in the Chinese DDW studies) and for communities with poor dietary variety.

When Purified Water Makes the Most Sense

There are situations where purified water is clearly the right call. If your source water is contaminated with lead, arsenic, agricultural chemicals, or industrial pollutants, RO or distillation provides a level of protection that carbon filters and boiling cannot match. In areas where tap water contains unsafe levels of PFAS, RO is one of the few household-accessible technologies that reliably reduces exposure.² During natural disasters or infrastructure failures that compromise water safety, purification technologies are genuinely life-saving.

Where the equation tilts the other way is in communities with well-maintained municipal water systems that already meet safety standards and add fluoride. In those settings, home RO systems remove a problem that largely does not exist while introducing the mineral-depletion issue and requiring ongoing maintenance to avoid microbial buildup. For a healthy adult eating a varied diet and living in a city with safe tap water, purified water is fine but offers limited advantage over what comes out of the faucet. For a family with young children, especially in a setting where dietary variety is limited, the mineral question deserves real consideration rather than being dismissed as a marketing angle for mineral water brands.