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What Is Reverse Osmosis Water? (And Should You Drink It?)

Updated October 2026·12 min read

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Reverse osmosis water (usually shortened to “RO water”) is water that’s been purified by forcing it through an extremely fine membrane that holds back most dissolved substances while letting water molecules through. It’s one of the more thorough water treatment methods available for the home, and it’s one of the methods used to make bottled water labeled “purified.” This guide explains what RO water actually is, how it’s made, what it removes, what it tastes like, and if you should drink it.

The gist

Reverse osmosis water is water that has been pushed under pressure through a semipermeable membrane fine enough to reject dissolved salts, metals, and many other contaminants while letting water molecules pass through. The result is water with far lower total dissolved solids (TDS) than what comes out of most taps; how much lower depends on the membrane and your water.

Because the membrane removes most dissolved substances, RO water is very clean. But it also loses the dissolved minerals (like calcium and magnesium) that give tap and spring water their taste. That’s why RO water can taste “flat,” and why many systems add a remineralization stage to put minerals back.

How Reverse Osmosis Works

To understand reverse osmosis, it helps to understand regular osmosis first.

Osmosis is a natural process: when you have pure water on one side of a semipermeable membrane and salty water on the other, water naturally flows toward the saltier side to balance the concentration. It’s how plant roots absorb water.

Reverse osmosis does the opposite. It uses pressure to force water the “wrong” way, from the concentrated (contaminated) side through the membrane to the pure side, leaving the contaminants behind. Your home’s water pressure (or a booster pump in tankless systems) provides the force.

A typical home RO system runs water through several stages:

  1. Sediment pre-filter: catches sand, rust, and dirt particles
  2. Carbon pre-filter(s): removes chlorine, taste, and odor (and protects the membrane)
  3. The RO membrane: the heart of the system, where dissolved solids and contaminants are rejected
  4. Post-carbon “polish” filter: final taste refinement
  5. (Optional) remineralization or alkaline stage: adds minerals back for taste
  6. (Optional) UV stage: a disinfection stage for bacteria and viruses, often chosen for well water

The contaminants the membrane rejects get flushed down the drain as “wastewater,” which is why RO systems use more water than they produce. Listed ratios vary a lot between systems; see our note on wastewater below.

What Reverse Osmosis Removes

This is RO’s main strength. Unlike a carbon filter (like a pitcher filter), which reduces chlorine and taste plus whatever specific contaminants that model is certified for, reverse osmosis reduces a wide range of dissolved contaminants. The specific reductions a given system is verified for are listed in its certification (NSF/ANSI 58 for RO systems):

  • Heavy metals: lead, arsenic, mercury, chromium, copper
  • Fluoride: RO is one of the few home methods that effectively removes it
  • Nitrates and nitrites: common in agricultural and well water
  • Total dissolved solids (TDS): salts and minerals
  • PFAS (“forever chemicals”): look for a PFOA/PFOS reduction claim on the certification
  • Microplastics: the membrane is a physical barrier to them
  • Chlorine and disinfection byproducts: mostly removed by the carbon stages
  • Many pesticides, herbicides, and pharmaceuticals

What RO does not reliably remove on its own: bacteria and viruses (the membrane helps but isn’t a certified microbiological barrier; that’s what the optional UV stage is for, and why many well-water users add one), and dissolved gases.

If you want to know what’s in your water before buying a system, start with your utility’s annual water quality report, or a certified lab test for a well. Home strip kits and TDS meters give a general picture but can’t establish whether specific contaminants such as fluoride, arsenic or PFAS are present at levels that matter; those need a test for that contaminant. See our water testing guide.

Here’s how RO handles each major contaminant. We don’t quote percentages because they vary by system; a system’s certification lists the reductions it has been verified for:

Contaminant How RO handles it
Lead Reduced by the membrane; check for a lead-reduction claim
Arsenic Reduced by the membrane; check for an arsenic-reduction claim
Fluoride Reduced by the membrane; NSF/ANSI 58 includes an optional fluoride claim
Nitrates Reduced by the membrane; check for a nitrate claim
PFAS (“forever chemicals”) Reduced; check for a PFOA/PFOS claim
Sodium / salt Reduced by the membrane
Total dissolved solids (TDS) Reduced; NSF/ANSI 58 certifies TDS reduction
Chlorine & taste Removed mainly by the carbon stages (NSF/ANSI 42 covers chlorine, taste and odor)
Microplastics Physically blocked; NSF/ANSI 401 includes a microplastics claim
Bacteria & viruses Reduced, but not a certified barrier. Add a UV stage

Actual performance varies with water chemistry, temperature, pressure, and membrane condition, which is why maintenance matters.

What Does Reverse Osmosis Water Taste Like?

RO water is commonly described as clean and neutral-tasting, without the chlorine taste, metallic notes, or hardness that tap water can have.

However, some people find pure RO water tastes “flat” or “empty.” That’s because the membrane strips out the dissolved minerals (calcium, magnesium, bicarbonates) that give water its familiar taste. It’s the same reason distilled water tastes bland.

The fix is remineralization: an extra filter stage that adds a small amount of minerals back, restoring a more natural, slightly alkaline taste. Many systems include this:

If you’ve tried RO water and found it flat, a remineralizing system is the usual fix. We cover the taste-and-minerals question in depth in Is Reverse Osmosis Water Good for You?.

Is Reverse Osmosis Water Safe to Drink?

RO water is widely used for drinking. Reverse osmosis is also one of the methods used to make bottled “purified” water, and it is used in laboratories and food production.

The one nuance people raise is mineral content. Because RO removes the small amounts of beneficial minerals (calcium, magnesium) along with the contaminants, some worry about “demineralized” water. For most people, food rather than drinking water is the main source of these minerals, though how much your tap water contributes depends on its hardness. If you prefer, a remineralizing system adds some minerals (and the taste) back; if you have a specific health concern, ask your doctor.

We cover the health debate, including what the World Health Organization has said about demineralized water and who might want remineralization, in our companion guide, Is Reverse Osmosis Water Good for You?.

Reverse Osmosis vs Other Water Types

How does RO water compare to the alternatives?

  • vs Tap water: RO is much lower in dissolved substances. It reduces the dissolved contaminants tap water can carry (lead, fluoride, nitrates, PFAS). Tap water retains its natural minerals; RO water removes them (unless remineralized).
  • vs Carbon-filtered (pitcher/faucet filters): Carbon filters reduce chlorine and taste, and some models are certified for specific contaminants such as lead or PFOA/PFOS, but they leave most dissolved solids, including fluoride and nitrate, behind. RO reduces a wider range of dissolved contaminants.
  • vs Distilled water: Both are highly purified and demineralized. Distillation boils and re-condenses water; RO filters it. They’re comparably pure, but RO is more practical for home use and doesn’t boil water.
  • vs Spring/mineral water: Spring water retains natural minerals (and their taste) but isn’t purified of all contaminants. RO water is purer but mineral-free unless remineralized.

For a head-to-head on form factors, see our whole-house vs under-sink RO guide.

At a glance, here’s how RO compares to the other common ways to treat home water:

Method What it removes Keeps minerals? Best for
Reverse osmosis Dissolved solids, metals, fluoride, nitrates, PFAS, more No (unless remineralized) Thorough, practical drinking-water treatment
Carbon filter (Brita / faucet) Chlorine, taste, some organics Yes Depends on the model: standard units target chlorine and taste; some carbon blocks are certified for lead, PFAS or other contaminants (check the data sheet)
Distillation Almost everything No Very high purity, but slow and energy-heavy
UV purifier Bacteria & viruses Yes Disinfection only; no dissolved-solid removal
Water softener Hardness (calcium / magnesium) Removes hardness Scale prevention, not drinking purity

The takeaway: only reverse osmosis and distillation remove the broad range of dissolved contaminants, and RO is the more practical for everyday home use.

The Wastewater Question

One honest downside of reverse osmosis: it produces wastewater. To purify water, the membrane flushes the rejected contaminants down the drain, so some water is “wasted.” RO’s reputation comes from systems that send several gallons to drain per gallon of pure water (1:3 or 1:4).

Many current systems list much better ratios. Several tankless systems list 2:1 or 3:1 pure-to-drain (for example, the Waterdrop G3P600 and G3P800), and APEC says its permeate-pump RO-PERM produces up to 80% less wastewater. It’s still a real consideration, especially if you’re on a well and pay to pump every gallon. Compare listed ratios when you shop.

How to Get Reverse Osmosis Water at Home

There are three main ways to get RO water in your home, depending on your situation:

  1. Under-sink RO system: installs under your kitchen sink with a dedicated faucet. The usual choice for homeowners. See our best reverse osmosis systems guide.
  2. Countertop RO system: no plumbing, sits on the counter, suited to renters and apartments. See our best countertop RO guide.
  3. Whole-house RO system: treats every tap in the home, for serious water-quality problems. See our whole-house RO guide and whole-house vs under-sink comparison.

For most people, an under-sink or countertop system is the right starting point. Our brand reviews (Waterdrop, iSpring, APEC, Express Water, and AquaTru) cover each major brand’s systems.

Frequently Asked Questions

Is reverse osmosis water the same as distilled water?

Not exactly, but they’re similar in purity. Both are highly purified and demineralized. Distilled water is made by boiling and re-condensing steam; RO water is made by filtering through a membrane. For drinking-water purposes, they’re comparably pure. RO is just more practical for home use.

Does reverse osmosis remove minerals from water?

Yes. The RO membrane removes dissolved minerals (calcium, magnesium) along with contaminants. This is what makes RO water taste “flat” to some people. A remineralization or alkaline stage adds minerals back for taste, and many systems include one.

Is reverse osmosis water acidic?

Slightly. With the minerals removed, pure RO water tends to be mildly acidic, as are many common beverages. If you prefer alkaline water, an alkaline/remineralizing system raises the pH back up.

Does reverse osmosis remove fluoride?

Yes. Reverse osmosis is one of the few home filtration methods that reduces fluoride. Standard carbon filters aren’t designed to. If fluoride removal is your goal, RO is the practical home option. See Does Reverse Osmosis Remove Fluoride? for details.

Is it OK to drink reverse osmosis water every day?

RO water is widely used for daily drinking. The main consideration is its low mineral content, which remineralization addresses if you prefer; for most people food is the larger mineral source. If you have a specific health condition, ask your doctor. See Is Reverse Osmosis Water Good for You? for the full picture.

Does reverse osmosis remove bacteria and viruses?

It reduces them, but a standard RO system is not a certified microbiological barrier. Some organisms can get through or colonize downstream of the membrane. City water is disinfected at the treatment plant. On well water or any untreated source, consider a UV stage, or a UV-equipped system like the iSpring RCC7AK-UV (iSpring lists alkaline plus an LED UV stage).

Does reverse osmosis remove chlorine?

Yes. The carbon pre-filter stages remove chlorine and its taste and odor before the water even reaches the membrane (chlorine is removed partly to protect the membrane itself). NSF/ANSI 42 is the standard that covers chlorine, taste and odor claims.

How long do reverse osmosis filters last?

It depends on the system and your water. As an example, iSpring’s RO500AK listing gives 6 months for the pre-filter, 12 months for the post-filter and 24 months for the RO membrane. Follow your manual, and see our maintenance guide for the full schedule.

Is reverse osmosis water the same as deionized (DI) water?

Not quite. Deionized water is run through ion-exchange resins to strip out remaining ions. It’s used in labs and aquariums. High-purity setups often pair the two (RO/DI). Home drinking-water systems use RO without the DI stage.

Bottom Line

Reverse osmosis water is water purified by forcing it through an ultra-fine membrane that removes most dissolved contaminants: heavy metals, fluoride, nitrates, PFAS, microplastics, and more (check a system’s certification for specific claims). The main trade-off is that it also removes minerals, which makes it taste flat to some people. A remineralizing system fixes that.

If you’re ready to get RO water at home, start with our best reverse osmosis systems guide for under-sink picks, or the best countertop RO guide if you rent. And if you’re weighing the health angle, read Is Reverse Osmosis Water Good for You? next.

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Primary sources

Check certifications and water-quality rules yourself: