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What’s the difference between reverse osmosis and distilled water?
The difference between reverse osmosis vs distilled water is how the water is cleaned. Distillation boils water and collects the steam, leaving minerals and most contaminants behind. Reverse osmosis pushes water through a membrane that holds back most dissolved solids. Distillation removes minerals most effectively, according to the EPA, but RO is faster, uses no heat, and costs less to run. For drinking, both remove most of what people worry about. For appliances that call for distilled water, RO is a close substitute for most uses.
| Reverse osmosis | Distillation | |
|---|---|---|
| How it works | Membrane under water pressure | Boils water, condenses the steam |
| Minerals left | Low; at least 75% of dissolved solids removed in certified systems | Lowest; removes minerals most effectively, per the EPA |
| Speed | About 25 gallons a day for certified under-sink systems | About 4 hours per gallon for a countertop distiller |
| Running cost | Filters and membrane; some water to the drain | Electricity, about $0.58 a gallon at average US prices |
| Certification | NSF/ANSI 58, with each contaminant claim listed | NSF/ANSI 62; we found no countertop distiller on NSF International’s listings |
| Weak spot | Wastewater; membrane wears over time | Some volatile chemicals boil over with the steam |
Is reverse osmosis water the same as distilled water?
No. Both are sold as “purified water,” but under FDA bottled water rules, water may be labeled “distilled” only if it was made by distillation. RO water is labeled “reverse osmosis water.” The EPA says distillation removes minerals most effectively, and water demineralized by RO or deionization would, on average, be expected to hold more minerals than distilled water. In practice, the two are close, and both are far lower in minerals than tap or spring water.
How does each one work?
Reverse osmosis: Household pressure, or a pump in countertop units, pushes water through a semipermeable membrane. Water molecules pass; most dissolved salts, metals, and minerals don’t, and they’re flushed to the drain. Carbon stages before and after the membrane handle chlorine and many organic chemicals. See how reverse osmosis works.
Distillation: A heating element boils the water, the steam rises into a cooling coil, and it condenses into a collection jug. Minerals, metals, and most other contaminants stay behind in the boiling chamber, which needs regular descaling.
What do reverse osmosis and distillation remove?
The CDC lists both as removing parasites, bacteria, and viruses. They differ on chemicals:
| Contaminant | Reverse osmosis | Distillation |
|---|---|---|
| Minerals and TDS | Removes most | Removes nearly all |
| Lead, arsenic, nitrate | Reduces; check the system’s certified claims | Removes, per the CDC |
| Fluoride | Reduces in systems certified for it | Removes most, per the ADA |
| Chlorine and VOCs | Carbon stages reduce them; some systems are certified for VOCs | Doesn’t remove some volatile organic compounds, per the CDC |
| Bacteria and viruses | Removes, per the CDC | Removes, per the CDC, but bacteria can grow on the cooling coils when idle |
An RO system is only as good as its certified claims. NSF/ANSI 58 requires TDS reduction; lead, arsenic, fluoride, and the rest are optional claims, so check the certifier’s listing for the exact model. See does reverse osmosis remove fluoride?
Which costs less to make at home?
Reverse osmosis, in most homes. An 800-watt countertop distiller takes about 4 hours per gallon, or about 3.2 kWh. At the EIA’s projected 2026 average residential price of 18.2 cents per kWh, that’s about $0.58 a gallon in electricity alone, before carbon post-filters and descaler.
RO filters cost from about $0.17 a gallon (AquaTru Classic) to about $0.33 (AquaTru Carafe) at the makers’ prices, and the under-sink systems we’ve scored cost about $60 to $160 a year in filters. RO also sends water to the drain: The EPA says a typical system wastes five gallons or more per gallon of treated water, and systems with the EPA WaterSense label must reach at least 30% efficiency, or about 2.3 gallons to the drain per gallon.
Which is better for drinking water?
For most homes, reverse osmosis. It makes more water, faster, from a dedicated faucet or a countertop unit, and certified systems list exactly what they reduce. Distillation suits small daily amounts, homes without room for RO, or water with a contaminant RO isn’t certified for, as long as it isn’t a volatile chemical.
Both remove most of the calcium and magnesium in your water, which changes the taste. Some RO systems add minerals back after the membrane; for distilled water, see how to remineralize water.
Can you use RO water instead of distilled water?
For most uses, yes. The EPA recommends low-mineral water such as distilled water for ultrasonic humidifiers, and names water demineralized by RO as the next best option. For a CPAP, follow the maker: Philips says distilled water only, while ResMed allows tap water but recommends distilled. Where a manual or lab method calls for distilled water only, use distilled water. Our guide to substitutes for distilled water covers each use.
Which reverse osmosis systems do we recommend?
Ranked by our overall score. Each is certified under NSF/ANSI 58 for TDS, lead, and fluoride. We found no countertop distiller on NSF International’s NSF/ANSI 62 listings, so we don’t rank distillers. How we score
| # | System | Score | Certified by | Lead | PFAS | Fluoride | Running cost | Price |
|---|---|---|---|---|---|---|---|---|
| 01 | AquaTru CarafeBest overall, no plumbingCountertop RO | 4.6 | IAPMO R&T | Certified | Certified | Certified | $0.33/gal | $356.25on Amazon › |
| 02 | Waterdrop G3P800Best under-sink, tanklessUnder-sink RO | 4.3 | IAPMO R&T | Certified | Certified | Certified | About $160/yr | $849.00on Amazon › |
| 03 | APEC RO-90Certified for lessUnder-sink RO | 4.2 | WQA | Certified | No | Certified | $60 to $75/yr | $219.16on Amazon › |
Certified: Certified by an independent body (named in each pick). Lab test: Tested by a named independent lab, not certified. Claim: The maker's claim, not certified. No: No claim. PFAS means PFOA/PFOS, or Total PFAS where the pick says so.
Common questions
Is distilled water purer than reverse osmosis water?
Usually, by a small margin. The EPA says distillation removes minerals most effectively, and RO water would, on average, hold more. But distillation doesn’t remove some volatile organic compounds, which an RO system’s carbon stages can reduce.
Is RO water distilled water?
No. Both are purified water, but only water made by distillation can be labeled distilled under FDA rules.
Can I drink distilled water every day?
The CDC lists distillation as a home treatment method for drinking water. Distilled water has almost no minerals, so it tastes flat. If you want minerals in your water, add a remineralizing stage or drops.
Does reverse osmosis remove bacteria?
The CDC lists RO as removing bacteria, viruses, and parasites. During a boil water advisory, though, follow the advisory; see does a water filter work during a boil water advisory?
Is it cheaper to make distilled water or buy it?
A countertop distiller uses about $0.58 of electricity per gallon at average US prices. Compare that with what a gallon costs at your store, and add the distiller’s price and upkeep.
Sources
- CDC: About home water treatment systems
- EPA: Use and care of home humidifiers
- eCFR: 21 CFR 165.110, Bottled water
- EPA WaterSense: Point-of-use RO systems specification, supporting statement
- EIA: Short-Term Energy Outlook, electricity (October 2026)
- NSF International drinking water treatment listings (NSF/ANSI 58 and 62)
- IAPMO R&T product listing directory (AquaTru, Waterdrop)
- WQA certified product listings (APEC)
- American Dental Association: Fluoridation Facts, home water treatment
- Waterwise 4000 distiller specifications (800 W, 1 gallon per 4-hour cycle)
- Philips DreamStation humidifier manual; ResMed humidifier setup guide
Prices as of October 14, 2026. Product prices and availability are accurate as of the date/time indicated and are subject to change. As an Amazon Associate we earn from qualifying purchases.