Is Reverse Osmosis Water Good for You? A Practical Answer

Reverse osmosis water is safe to drink for most households, and it is mainly a contaminant-removal choice. Whether losing the minerals matters depends on what your diet already supplies.

Reverse osmosis (RO) pushes water through a semipermeable membrane under pressure. Most home systems add carbon filters before and after that membrane. A point-of-use RO system treats only the tap it is plumbed to, usually the kitchen drinking-water tap, not the whole house.

The sections below run from the mineral question to the certificate, then to the water test. The last sections cover trade-offs and the groups who should talk with a clinician first.

What Reverse Osmosis Removes and What It Leaves Behind

Reverse osmosis pushes water through a semipermeable membrane under pressure. Most home systems add carbon filters before and after the membrane, so the membrane is one stage of several.

NSF International (NSF) certifies membranes contaminant by contaminant. A unit certified for one contaminant is not certified for the others. The what reverse osmosis removes page covers the removal side in more detail.

Reverse osmosis water is safe to drink for most households, and the system is mainly a contaminant-removal choice. Low mineral content matters little for people whose diet supplies calcium and magnesium. Whether that describes your household depends on the sections below.

Why Losing the Minerals Matters Less When Food Supplies Them

The World Health Organization (WHO) published a review called Nutrients in Drinking-water. Its framing is that food supplies most dietary calcium and magnesium for most people. Water matters more where diets are low in those minerals (WHO).

RO water has very little dissolved mineral content.

Whether your diet is low in calcium or magnesium is a question about food. The clinician section below covers when to talk with a clinician about the water.

Taste, Acidity, and Remineralizing Cartridges

RO water is often slightly acidic, and it has little buffering because it has very little dissolved mineral content.

A remineralizing cartridge placed after the membrane adds calcium and magnesium back to the water. These cartridges are sold as an add-on.

If taste or minerals matter to you, the remineralizing stage changes the water after the membrane. A carbon-only unit is the other route covered in the carbon section below.

Read the NSF/ANSI 58 Certificate for the Contaminants It Names

NSF/ANSI 58 is the standard for point-of-use reverse osmosis drinking water treatment systems.

A certification covers only the contaminants named on the certificate. A unit certified to NSF/ANSI 58 for one contaminant has not been shown to remove the others.

Use the certificate as the deciding document for the purchase. Find the contaminant in your water result, then find a unit whose certificate names that same contaminant. Start with the water test kit page.

When Reverse Osmosis Is the Right Tool

Reverse osmosis is the right tool when your water result shows a contaminant that the unit's certificate names. Lead and per- and polyfluoroalkyl substances (PFAS) each have their own pages: lead in water and PFAS water filters.

For public water systems, the U.S. Environmental Protection Agency (EPA) sets a maximum contaminant level (MCL), a legal limit, of 10 milligrams per liter measured as nitrogen for nitrate. The same agency sets 10 micrograms per liter as the legal limit for arsenic.

Those limits are written for public drinking water, so a private well is a different situation. The testing section below covers private wells.

When a Carbon Filter Is Enough

A carbon-only unit is worth comparing when its certificate names the contaminant your test found. Most reverse osmosis systems already use carbon before and after the membrane, so carbon is part of the RO design.

If the test finds a contaminant that no carbon-only certificate names, the membrane stage is then the question. The certificate decides it.

The under sink water filter page covers the carbon-only side of the choice.

Drain Water and Point-of-Use Coverage Are the Trade-Offs

Reverse osmosis sends part of the incoming water to the drain as concentrate. The ratio varies by model. Ask the maker for the ratio on the model you are considering.

A point-of-use system treats only the tap it is plumbed to, usually the kitchen drinking-water tap. The rest of the house is not treated.

The reverse osmosis system page covers the system as a whole. For the distilled water side of the choice, see reverse osmosis vs distilled water.

Infants and Restricted Diets Need a Clinician's Input

The Centers for Disease Control and Prevention (CDC) identifies nitrate as a particular concern for infants under six months, and private wells are a common place to find it. Anyone mixing infant formula with RO water should talk with a clinician about that water first.

People on a mineral-restricted or sodium-sensitive diet should also talk with a clinician before relying on RO water. RO water has very little dissolved mineral content.

The verdict in the opening section does not cover these groups. Their situation calls for individual advice, not a general answer.

Test the Water Before Choosing a Unit

Private wells are not regulated by EPA, and their owners are responsible for testing (EPA). A public water utility publishes an annual consumer confidence report (EPA).

Work through three steps before buying:

• Get a result for the contaminant you suspect, starting from the water test kit page.
• Match that contaminant to a unit whose certificate names it, and skip units whose certificates name other contaminants only.
• Ask the maker for the drain ratio on that model, since the ratio varies by model.
• The verdict changes if a test finds a contaminant that no certificate you can find names, or if you fall into one of the clinician groups above. Start with the test.