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

By the PureFlow Lab Team·Updated June 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 strains out nearly everything except the water molecules themselves. It’s one of the most thorough water purification methods available for the home, and it’s what bottled “purified” water usually is. This guide explains what RO water actually is, how it’s made, what it removes, what it tastes like, and whether you should drink it.

The Short Answer

Reverse osmosis water is water that has been pushed under pressure through a semipermeable membrane with pores so small (about 0.0001 microns) that they block dissolved salts, metals, and most other contaminants while letting pure water molecules pass through. The result is water that’s typically 90-99% free of total dissolved solids (TDS) — far purer than what comes out of most taps.

Because the membrane removes nearly everything, 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 — sterilizes bacteria and viruses, important 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. Modern systems have improved this ratio significantly; see our note on wastewater below.

What Reverse Osmosis Removes

This is RO’s superpower. Unlike a simple carbon filter (like a basic pitcher filter), which mainly improves taste and removes chlorine, reverse osmosis removes a huge range of dissolved contaminants:

  • 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, reduced by 90-99%
  • PFAS (“forever chemicals”) — RO is among the most effective home methods
  • Microplastics — the membrane’s tiny pores block 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 well-water users need it), and dissolved gases.

If you want to know exactly what’s in your water before buying a system, a home water test kit (or your municipality’s annual water quality report) tells you which contaminants you actually need to target.

Here’s roughly how much of each major contaminant a healthy RO system removes:

Contaminant Typical RO reduction
Lead 95–99%
Arsenic 90–99%
Fluoride 85–95%
Nitrates 85–95%
PFAS (“forever chemicals”) 90–99%
Sodium / salt 90–98%
Total dissolved solids (TDS) 90–99%
Chlorine & taste ~98% (carbon stages)
Microplastics ~99%+
Bacteria & viruses Reduced, but not a certified barrier — add a UV stage

Exact figures vary with water chemistry, temperature, pressure, and membrane condition, but a well-maintained system reliably lands in these ranges.

What Does Reverse Osmosis Water Taste Like?

Most people describe RO water as clean, crisp, and “pure” — without the chlorine taste, metallic notes, or hardness that tap water can have. If your tap water tastes bad, RO water is usually a dramatic improvement.

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 solves it. We cover the taste-and-minerals question in depth in Is Reverse Osmosis Water Good for You?.

Is Reverse Osmosis Water Safe to Drink?

Yes. Reverse osmosis water is safe to drink and is, by most measures, among the cleanest water you can have at home. It’s the same purification method used for much commercial bottled “purified” water, in laboratories, and in many medical and food-production settings.

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. In practice, the minerals in drinking water contribute only a small fraction of your daily intake — the vast majority comes from food. For most people on a normal diet, drinking RO water is completely fine. If you prefer, a remineralizing system adds the minerals (and the taste) back.

We unpack 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 far purer — it removes 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 improve taste and remove chlorine but leave most dissolved solids, heavy metals, and fluoride behind. RO removes far more.
  • 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 far more practical and energy-efficient for home use.
  • 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) The most thorough drinking-water purification
Carbon filter (Brita / faucet) Chlorine, taste, some organics Yes Taste only — leaves most contaminants
Distillation Almost everything No Lab-grade 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 by far 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.” Older systems wasted 3-4 gallons per gallon of pure water (a 1:3 or 1:4 ratio).

Modern systems have improved this dramatically. Tankless systems commonly hit 2:1 or better, and APEC’s permeate-pump models cut waste by up to 80%. It’s still a real consideration — especially if you’re on a well and pay to pump every gallon — but it’s far less of a drawback than it used to be.

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 most popular, best value for homeowners. See our best reverse osmosis systems guide.
  2. Countertop RO system — no plumbing, fully portable, ideal for 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 — break down the best systems from each major brand.

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 far more practical and energy-efficient 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. Removing minerals lowers the pH a bit, so pure RO water is mildly acidic (around pH 6-7). This is harmless to drink. 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 effectively removes fluoride. Standard carbon filters do not. If fluoride removal is your goal, you specifically need RO. See Does Reverse Osmosis Remove Fluoride? for the full data.

Is it OK to drink reverse osmosis water every day?

Yes. RO water is safe for daily drinking and is among the cleanest water available at home. The only consideration is its low mineral content, which is easily addressed with remineralization if you prefer — and which matters little for people on a normal diet. 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. On chlorinated city water this rarely matters. On well water or any untreated source, add a UV sterilization stage, or buy a UV-equipped system like the iSpring RCC7AK-UV.

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). Reduction is typically around 98%.

How long do reverse osmosis filters last?

Pre-filters (sediment and carbon) usually last 6–12 months; the RO membrane lasts 2–4 years; the post-carbon polish filter about a year. Budget roughly $50–$120/year on replacements. See our installation guide for setup and upkeep.

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

Not quite. Deionized water is run through ion-exchange resins to strip out essentially all ions — even purer than RO, used in labs and aquariums. High-purity setups often pair the two (RO/DI). For drinking water, RO alone is more than enough.

Bottom Line

Reverse osmosis water is water purified by forcing it through an ultra-fine membrane that removes 90-99% of dissolved contaminants — heavy metals, fluoride, nitrates, PFAS, microplastics, and more. It’s clean, safe, and among the purest water you can get at home. The main trade-off is that it also removes beneficial minerals, which makes it taste flat to some people — easily solved with a remineralizing system.

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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