Yes. Reverse osmosis removes most dissolved minerals, including calcium and magnesium, along with contaminants, so RO water is low in minerals. For most people on a normal diet this matters little, because health authorities say food, not water, is the main mineral source.
Yes, reverse osmosis removes most dissolved minerals
A reverse osmosis system pushes water through a membrane with openings near 0.0001 micron wide, per the CDC. That is small enough to block most of what is dissolved in the water, including calcium and magnesium, the two minerals people usually mean when they say "healthy minerals."
The same fine membrane is why RO is so good at removing contaminants. The EPA notes that a point-of-use RO unit reduces lead, arsenic, nitrate, PFAS, volatile organic compounds, and many other dissolved substances, along with bacteria and viruses. The membrane does not sort "good" minerals from "bad" ones. It blocks dissolved solids broadly, so the calcium and magnesium leave with the contaminants.
The result is water with very low total dissolved solids, often called low-TDS water. In Phoenix, where city water runs roughly 10 to 16 grains per gallon of hardness, RO can take that down to a tiny fraction. So the premise of the question is correct. What matters next is whether that mineral loss actually affects your health, and the answer there is more reassuring.
Why the mineral loss is usually minor for your health
For someone eating a normal diet, the minerals lost from drinking RO water are a small slice of daily intake. That is because most dietary calcium and magnesium come from food, not water. The World Health Organization is direct about this. In its report on calcium and magnesium in drinking water, WHO states:
"In most cases, food is the principal source of both calcium and magnesium."
The NIH Office of Dietary Supplements backs this up by pointing to food as the main way people meet their needs. Calcium comes from dairy, leafy greens, and fortified foods. Magnesium comes from nuts, seeds, whole grains, beans, and greens. The amount in a few glasses of tap water is small next to a day's worth of meals, so removing it changes the total very little for most healthy adults.
To put it in scale, the calcium an adult needs in a day is on the order of a thousand milligrams, and most of that is met through food. The calcium and magnesium in tap water vary a lot by region and are a modest contributor at best. So when an RO unit takes those minerals out of your drinking water, it is removing a small part of an already small share. That is why the framing matters. The question is not whether RO removes minerals, since it clearly does, but whether that loss is large enough to matter for a person eating regular meals. For most people, it is not.
WHO has also discussed possible concerns with water that has very low mineral content, including taste and the loss of any contribution drinking water might make to mineral intake. The organization has noted potential benefit in adding minerals back, especially for infants whose formula and fluids make up most of what they consume. This is a measured point, not an alarm. If you have a specific health condition, a restricted diet, or you are preparing infant formula, that is a good reason to talk with your doctor about your own situation. This page is general information, not medical advice for your individual case.
Why RO water tastes flat and how remineralization fixes it
The minerals RO removes are also part of what gives water its taste. Strip them out and the water can taste flat, dull, or slightly off compared to the mineral-rich tap water many people are used to. This is a common reason new RO owners are surprised by the flavor, even though the water is clean and safe to drink.
The usual fix is a remineralization or alkalizing post-filter. This stage sits after the membrane and adds a small, controlled amount of calcium and magnesium back into the finished water. It puts back enough to improve the taste and raise the pH a bit, without undoing the contaminant removal that made you want RO in the first place. Many under-sink systems include this stage, and it can be added to ones that do not.
So the taste complaint and the "missing minerals" worry have the same simple answer. A remineralization stage addresses both at once, which is why it is such a popular add-on. It does not make the water meaningfully more nutritious in diet terms, but it does make it taste like the water most people expect.
Why low-mineral water matters more for whole-house RO
The mineral question changes shape depending on whether you are treating one tap or the whole house. For a standard under-sink RO unit that feeds a single drinking faucet, the low-mineral output only touches the water you drink and cook with. The taste fix is the main concern, and remineralization handles it.
A whole-house RO system is a different story. It treats every drop in the home, and very low-mineral water can be aggressive, meaning it tends to pull metals from the surfaces it touches. Over time, water with almost no minerals can be harder on metal plumbing and fixtures than balanced water. For this reason, whole-house RO setups typically need a remineralization or pH-correction stage not only for taste but to protect the home's pipes. This is one of several reasons most homes do not need whole-house RO, since you generally do not need RO-grade water for showering, laundry, or toilets. For more on that trade-off, see our page on under-sink versus whole-house reverse osmosis.
If your main goal is to stop scale from hard water across the whole house, RO is not the right tool. That job belongs to a water softener, which removes hardness from all the water in the home. RO and softeners do different jobs, and our page on reverse osmosis versus a water softener walks through which one fits which problem.
The takeaway on RO and your minerals
Reverse osmosis does remove most dissolved minerals, including calcium and magnesium, because the membrane blocks dissolved solids across the board. That is the same property that makes RO so effective at removing lead, arsenic, nitrate, and other contaminants. The mineral loss is real, but for a healthy person eating a normal diet it is a minor change, since health authorities agree that food is the main source of these minerals.
The two practical effects worth acting on are taste and, for whole-house systems, plumbing protection. A remineralization post-filter handles both by adding a measured amount of calcium and magnesium back into the treated water. It is a standard, low-cost addition, and for whole-house RO it is close to a must-have.
If you have a medical condition, a special diet, or you are mixing infant formula, ask your doctor whether the mineral content of your drinking water is something you should plan around. For the water side, regular filter and membrane changes keep an RO system working as intended. Our guide to reverse osmosis filter replacement and maintenance covers the typical schedule, and HQ Plumbing & Air can install or service an RO system, including a remineralization stage, for homes and businesses across metro Phoenix.