Is reverse osmosis water bad for you? The "dead water" claim, minerals and adding them back

What reverse osmosis takes out

RO pushes water through a membrane with extremely small pores. According to the CDC, RO systems remove parasites, bacteria and viruses, plus chemicals like lead, copper, chromium, chloride and sodium. They can also reduce arsenic, fluoride, radium, sulfate, nitrate, calcium, magnesium and potassium. The CDC's advice is to check the system's label for what it's certified to remove.

So RO doesn't pick and choose. It removes what you don't want in your water and most of the minerals too. That second part is where the worry comes from. For a closer look at the removal side, see does RO remove PFAS, fluoride and microplastics? and how reverse osmosis works.

The "dead water" claim, checked

You'll see RO water called "dead," "empty" or "hungry" water, with claims that it pulls minerals out of your body, weakens bones and teeth, and needs to be fixed before you drink it. Most of those pages are selling a fix.

Here's what holds up and what doesn't:

• It has few minerals. True. That's the point of RO.
• You'll miss out on minerals you need. Not for most people. Food is the main source (more below).
• It pulls minerals out of your body. We found no good human evidence for this. A 2023 narrative review in Cureus argues that low-mineral water harms bones and teeth, but it's a narrative review, not a systematic one. It leans on the 2005 WHO chapter covered below and a few observational studies, which show a link, not cause and effect.
• It pulls metals out of pipes and fittings. True, and this is the part worth your attention. More on that in the acidity section below.

What the WHO paper on demineralized water says

The paper most "RO is bad" articles point to is a chapter called "Health risks from drinking demineralised water," by Czech public health researcher František Kožíšek, published in a 2005 World Health Organization book, Nutrients in Drinking-water. It's worth reading fairly, because it raises real points.

What it says. The chapter covers water with almost no minerals, such as RO, distilled or deionized water. It argues that this kind of water:

• is corrosive and can pick up metals from pipes and fittings if it isn't treated first,
• tastes flat,
• may change the body's water and salt balance and increase urination, based mostly on animal studies and older research,
• supplies little or no calcium and magnesium, and
• can pull more minerals out of food when you cook with it, based on older studies.

It also cites a 1980 WHO report, based on studies in rats, dogs and human volunteers, that recommended at least 100 mg/L of dissolved minerals in drinking water and at least 30 mg/L of calcium in desalinated water. And it's honest about gaps: it says a direct harmful effect on the stomach and gut lining had not been clearly shown.

Its limits. In 2020, Germany's Federal Institute for Risk Assessment (BfR) reviewed this question for mineral water with very low mineral content. It found that the chapter "cites various, mostly older animal and human studies written in Russian," that its statements "are outdated," and that later WHO reports "do no longer mention the results of these studies" (BfR, 2020). The BfR also notes that "only few scientific studies are available," so there are real knowledge gaps.

The WHO's own drinking water guidelines, as quoted by the BfR, say the evidence linking minerals in water to heart health "is being debated and does not prove causality," and that there isn't enough data to set a minimum level. So no minimum calcium or magnesium level is set for drinking water.

What applies to you. Two points from the chapter still matter for a normal diet:

1. 1Corrosion is real. Low-mineral water can pull metals from plumbing after the filter. That's an equipment problem, not a reason to avoid RO water. Check refill machines before you fill (see below).
2. 2Water can be a mineral source for some people. A 2009 WHO report says mineral-rich water can add meaningfully to intake in some populations, and that many people don't get enough calcium or magnesium from their diets. If your diet is short on these, it's worth fixing, and food is the reliable way.

The BfR's bottom line: "it can be assumed that mineral, spring and table water with very low mineral content does not have any long-term adverse effects on health," as long as you eat "a balanced diet and normal drinking quantities."

Where your minerals really come from

"Food is the principal source of both calcium and magnesium," according to the WHO. The BfR agrees: "A lower mineral intake due to the consumption of water with very low mineral content can be compensated by the intake of minerals from other types of food."

Here's how everyday foods compare, using figures from the National Institutes of Health:

Sources: NIH calcium fact sheet and NIH magnesium fact sheet. Blank cells mean we didn't list that mineral for that food, not that it's zero.

Water varies a lot. The NIH says magnesium in water ranges from about 1 mg/L to more than 120 mg/L depending on the source and brand. So mineral-rich water can help, but it isn't something you can count on, and RO water was never going to be your main source anyway.

One honest caveat: the NIH reports that 48% of Americans get less magnesium from food and drinks than they should. If that's you, the fix is the same with or without RO: more seeds, nuts, beans, greens and whole grains, or a talk with your doctor about whether you need a supplement.

What about your heart?

This is the strongest argument on the "keep the minerals" side, so here it is straight. A 2016 analysis of 10 studies found that people whose drinking water had more magnesium had about an 11% lower risk of dying from heart disease. But the studies were observational, nine of the 10 were from Europe, and the results varied a lot from study to study. That shows a link, not cause and effect, which is why the WHO says the evidence "does not prove causality" and sets no minimum.

If heart health is your reason for caring about minerals, magnesium from food counts the same. The BfR says research so far "has not shown that the actual source (fluid or solid food) of the mineral is important."

Is RO water bad for your kidneys?

We found no study showing that RO water harms healthy kidneys. For kidney stones, the NIDDK (part of the NIH) says "Drinking enough liquid, mainly water, is the most important thing you can do to prevent kidney stones." RO water counts.

If you have chronic kidney disease, the question is usually how much you drink, not what kind of water. The NIDDK says people with CKD may need to limit liquids because damaged kidneys can't remove extra fluid. Ask your doctor how much is right for you.

Is RO water acidic?

It can be slightly. RO water has very little of the minerals that buffer pH, so it's "low in alkalinity and pH," as researchers in a 2026 study of US refill kiosks put it. The bigger concern is what that does to plumbing.

The EPA suggests a pH of 6.5 to 8.5 for drinking water. That's a non-mandatory guideline for taste and corrosion: low pH can taste bitter or metallic and corrode pipes. That corrosion is what the kiosk study found. Lead showed up in water from most of the machines it tested, and the researchers linked it to metal parts placed after the RO step. Read the details and a quick pre-fill checklist in are grocery store refill stations safe?

Fluoride and your teeth

RO can reduce fluoride, which the CDC notes helps prevent cavities. If RO water is most of what you drink, tell your dentist. They can tell you whether fluoride toothpaste is enough or whether you'd benefit from something more.

Should you add minerals back?

For most people, no. It's worth it if:

• You don't like the taste. Water with almost no minerals tastes flat to a lot of people. If a little mineral content helps you drink more water, that's a win.
• RO is nearly all you drink and your diet is limited. The BfR says these groups "should pay attention to their total daily intake of certain essential minerals if they use low mineral content water as their primary source of fluids": people with very unbalanced diets, people who avoid whole food groups (for example vegans or people with lactose intolerance), people fasting for long periods, and pregnant or breastfeeding women. Food and your doctor come first here. Minerals in water are a small top-up at best.
• You exercise hard for long stretches. For exercise over about 1.5 hours, the BfR says very low-mineral water is "not recommended as the sole or primary type of beverage."

Here's how the common options compare. Prices are list prices we saw on the seller's page or in our directory on November 3, 2026. We haven't tested these products, and we name them as examples, not endorsements.

What we'd pick. If you have a home RO system and want minerals for taste, add a remineralizing cartridge. It's the one option you don't have to think about. If you fill jugs at a refill station, buy alkaline water at the same machine when you want it, or keep a bottle of drops for the jug at home and start with a few drops. And if your reason is health, not taste, put the effort into food. That's where the meaningful amounts are: one 8 oz cup of plain low-fat yogurt has 415 mg of calcium, per the NIH.

What it costs at the machine. More than 450 stations in our directory list alkaline water, and almost all of them list RO too. Most alkaline listings are $1.29 a gallon, nearly all at Whole Foods machines, while most RO listings are $0.50. That's $0.79 more per gallon, or about $290 more a year at a gallon a day. Learn more about alkaline water and hydrogen water, the other upgrade you'll see at some machines.

If you'd rather have water with natural minerals, more than 1,200 stations in our directory list spring water, and you can compare the two in spring water vs. filtered water. Want a rough read on how much is dissolved in your water? Here's what a TDS meter can and can't tell you.

The case for filtered water

Put the two sides next to each other. RO takes out minerals you can easily get from a handful of almonds or a cup of yogurt. It also removes lead, copper, bacteria and viruses, and reduces things like arsenic and nitrate, per the CDC. You can't fix those with food. That trade is why filtered water makes sense for drinking, as long as the system or machine is well maintained.

You also don't need to buy a system to get it. Most refill stations we list post $0.50 a gallon for RO. Here's whether reverse osmosis is worth it at home versus at a station, and what a 5-gallon refill really costs compared with bottled water.

FAQ

Is it safe to drink RO water every day?

Yes, for healthy people with a balanced diet. Germany's BfR found no expected long-term harm from very low-mineral water "assuming a balanced diet and normal drinking quantities." Keep any home system's filters on schedule and check refill machines before you fill.

Is RO water bad for your kidneys?

We found no study showing that RO water harms healthy kidneys. The NIDDK says drinking enough liquid, mainly water, is the most important thing you can do to prevent kidney stones. If you have kidney disease, ask your doctor how much fluid you should drink.

Do I need to add minerals back to RO water?

Usually not. Most calcium and magnesium comes from food. Adding minerals is worth it if you dislike the flat taste, or if RO is nearly all you drink and your diet is limited. A remineralizing cartridge, mineral drops or alkaline water at the machine all work.

Is RO water acidic?

It can be slightly, because it has few of the minerals that buffer pH. That isn't a problem for your body, but it can corrode metal plumbing, which is why refill machine maintenance matters.

Does reverse osmosis remove minerals?

Yes. RO removes most dissolved minerals, including calcium, magnesium and potassium, along with contaminants like lead and nitrate. That's also why RO water reads low on a TDS meter.

Can I use RO water for baby formula?

The BfR says preparing industrially made infant formula with very low-mineral water, following the instructions, does not pose a health risk, because the formula supplies the minerals. Ask your pediatrician about water for your baby.

Why does RO water taste flat?

Minerals give water much of its taste, and RO removes most of them. A remineralizing cartridge, a few mineral drops or alkaline water at the machine can help.