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If you are weighing reverse osmosis vs distilled water for your kitchen, here is the short answer: both make low-mineral drinking water, but they get there in very different ways. For a household that wants steady drinking and cooking water at a dedicated tap, a suitably sized reverse osmosis system is often more convenient than a small batch distiller. A water distiller can still supply your drinking water if its output, energy use, and upkeep fit your routine, and purchased distilled water is the usual choice for devices that call for it.
Is RO Water the Same as Distilled Water?
No. RO and distillation are different processes that both reduce dissolved minerals, and distillation generally removes more of them, according to the EPA. Reverse osmosis pushes water through a semipermeable membrane, while distillation boils water and condenses the steam.
Total dissolved solids (TDS) is the amount of solids dissolved in water, mostly minerals such as calcium, magnesium, and sodium. Our guide explains what a TDS reading measures. RO output depends on your feed water, the system, and operating conditions, and a remineralization stage raises the final reading.
A handheld TDS meter estimates dissolved content. It does not identify individual contaminants, confirm that water is safe, or prove that water is distilled. The EPA treats TDS as a secondary, aesthetic standard, not a safety test.
Reverse Osmosis vs Distilled Water Side by Side
| Factor | Under-sink RO system | Countertop water distiller |
|---|---|---|
| How it works | Water pressure pushes water through a membrane, with sediment and carbon stages | Boils water, condenses the steam, and collects it one batch at a time |
| Mineral content | Low; higher if a remineralization stage is added | Low; generally lower than RO |
| Contaminant reduction | Reduces many dissolved solids and contaminants; claims vary by model | Reduces many minerals and chemicals; claims vary by model |
| What it can miss on its own | Some VOCs, solvents, and pesticides can pass the membrane | Some VOCs and solvents can carry over with the steam |
| Production | Stored tank water or rated tankless flow; the tank refills over time | Batches that often take hours per gallon |
| Energy | None for conventional pressure-driven units; electric pumps and UV lamps need power | Electricity for every gallon |
| Water sent to the drain | Reject water whenever it is producing | No continuous reject stream; residue and rinse water |
| Cost to own | Equipment, installation, filters, membrane | Unit, electricity, cleaning supplies, post-filters |
| Maintenance | Filter and membrane changes, periodic sanitizing | Boiler rinsing, descaling, container cleaning, post-filter changes |
| Taste | Can taste flat; remineralization changes that | Often described as flat |
| Relevant standard | NSF/ANSI 58 | NSF/ANSI 62 |
| Typical best fit | Steady drinking and cooking water at the kitchen tap | Smaller daily volumes, or homes where RO isn’t practical |
In the distillation vs. reverse osmosis matchup, distillation usually removes more dissolved material, while RO usually wins on convenience, output, and energy use. Water sent to the drain is where RO gives ground.
How Reverse Osmosis and Distillation Work
How a Reverse Osmosis System Works
A typical under-sink RO system uses your household water pressure to push tap water through a series of stages:
- Sediment prefilter: catches sand, rust, and other particles.
- Carbon prefilter: reduces chlorine and other compounds that can damage the membrane.
- RO membrane: separates much of the dissolved material and sends it to the drain as reject water.
- Storage tank or tankless design: a small pressurized tank holds treated water, while tankless RO units produce on demand within a rated flow.
- Carbon post-filter: a final activated carbon filter polishes the water before it reaches a dedicated faucet at your sink.
Countertop RO units also exist for homes without space under the sink.
How a Water Distiller Works
A countertop distiller heats water in a boiling chamber until it turns to steam. The steam travels into a condensing coil, cools back into liquid through condensation, and drips into a collection container. Minerals and many other dissolved substances stay behind as residue in the chamber.
Some models add a carbon post-filter or a gas vent. Automatic models that refill and run on their own are also available as an alternative to batch units.
The core difference is simple: RO uses pressure and a membrane, and distillation uses heat and a phase change. For a broader look at the terms, see how purification differs from filtration.
What Each Method Removes and What It Can Miss
The CDC describes the general capabilities of each process:
- Distillation removes many chemicals, including arsenic, lead, nitrate, sodium, calcium, and magnesium.
- Reverse osmosis removes lead, copper, chromium, chloride, and sodium, and may also reduce arsenic, fluoride, nitrate, and others.
The CDC also lists both methods as able to reduce parasites, bacteria, and viruses as a general process capability. That is not the same as a certified claim for a particular product. The same CDC page notes that bacteria can grow on a distiller’s cooling coils when it sits unused.
Neither method is complete on its own. The CDC says distillation does not remove some volatile organic compounds (VOCs), solvents, and certain pesticides, and the University of Nebraska Extension notes that some pesticides, solvents, and VOCs are not removed by an RO membrane.
Carbon filtration stages and, in some distillers, venting can help with these compounds, but results depend on the compound, the design, and maintenance.
Removal depends on the specific system. Look for certification to NSF/ANSI 58 for RO systems or NSF/ANSI 62 for distillers, then check the exact model’s listing on the certifier’s site, because certification covers only the contaminants listed for that model.
This comparison assumes treated municipal water from a public supply. Do not rely on a household RO system or distiller to override a boil-water advisory or to treat water from an unknown source.
Capacity, Energy, Cost and Upkeep
Production Capacity
An RO storage tank supplies stored water while the membrane refills it. Output and refill times vary by system, and tankless units have rated flow limits, so size the system for the maximum amount of water your household uses at one time, not just the daily total.
A countertop distiller works much more slowly. One countertop model, the Waterwise 4000, is rated at about 4 to 4.5 hours per gallon, and the University of Nebraska Extension reports that batch distillers generally produce 3 to 10 gallons per day. Allow extra time for cooling and cleaning between batches.
Energy Use
Conventional pressure-driven under-sink RO systems can operate without an electrical connection. Systems with electric booster pumps, UV lamps, or other powered components need electricity, while some permeate pumps are hydraulically powered and do not.
A distiller uses electricity for every gallon. You can estimate it with a simple formula: watts ÷ 1,000 × hours per gallon = kWh per gallon.
For the Waterwise 4000, rated at 800 watts, that works out to 800 ÷ 1,000 × 4 to 4.5 hours, or about 3.2 to 3.6 kWh per gallon. This is an estimate from rated power, and actual use varies. Multiply by your electricity rate to get your cost per gallon.
Water Sent to the Drain
The EPA WaterSense program says a typical point-of-use RO system sends five gallons or more of wastewater down the drain for every gallon of treated water it produces. WaterSense-labeled systems send 2.3 gallons or less per gallon produced. A countertop distiller has no continuous reject stream like RO, but it leaves residue that is rinsed out, and routine cleaning uses water.
Cost of Ownership
The table above lists the cost items for each system, and purchased distilled water has its own retail cost. Your total depends on daily volume; our breakdown of the long-term cost of an RO system covers the RO side.
Maintenance
RO systems need prefilter, post-filter, and membrane replacement, plus periodic sanitizing as the manufacturer directs. Distillers need boiler rinsing, descaling, collection-container cleaning, and carbon post-filter replacement where fitted. The Waterwise 4000, for example, directs a boiler rinse after every cycle and a new carbon post-filter every two months or 60 to 80 gallons, whichever comes first. How often depends on the model, your water hardness, and how much you use it. Keep collected water in a clean, covered container, because low-mineral water can still be recontaminated.
How Arizona’s Hard Water Affects Both Methods
Here is what three Valley cities publish:
- Phoenix: The 2025 Water Quality Report lists hardness of 172 to 302 ppm (10 to 17.6 grains per gallon) and TDS of 464 to 716 ppm, with chlorine as the disinfectant.
- Mesa: The 2025 Water Quality Report lists TDS of 190 to 970 ppm and average hardness of about 12 gpg in the City Zone and 16 gpg in the Eastern and Southern Zones. Mesa lists chlorine and chlorine dioxide as disinfectants.
- Chandler: The city’s undated Water Quality FAQs put hardness at 5 to 20 gpg, averaging 16.5 gpg, with chlorine as the disinfectant.
An RO membrane removes a large share of the dissolved solids in these supplies, so RO water measures far lower than the tap, before any remineralization.
Hardness minerals can scale an RO membrane. Feed-water composition and operating conditions also affect performance, and TDS alone does not predict membrane life. Our guide to RO filter and membrane life in Phoenix covers what to expect.
Where the water analysis and equipment call for it, softener pretreatment can reduce scaling, but a softener does not lower total dissolved solids. Read more about pairing a water softener with RO. In a distiller, calcium and magnesium stay behind, so hard water means faster scale buildup and more frequent descaling.
Chlorine matters too. The University of Nebraska Extension notes that carbon prefilters protect thin-film RO membranes from chlorine, which is why they come before the membrane.
Utility reports give system-level ranges. The value at your tap can differ by source, season, service area, and any treatment in your home, so check your city’s latest water quality report or test your water.
Taste and the Low-Mineral Question
The University of Nebraska Extension notes that distilled water is often described as having a flat taste because minerals and some dissolved oxygen are removed. Background documents for the WHO drinking-water guidelines also note that very low-TDS water may taste flat or insipid.
RO water can taste similar, and remineralization stages change that, so it helps to know how to add minerals back to RO water. Taste is personal, so a glass of each side by side will tell you more than any description.
Online claims about low-mineral water and the body often lump RO and distilled water together. Both methods produce low-mineral water, so these claims do not separate one from the other, and mineral content alone does not show that either is healthier. If you have health questions about drinking RO water, we cover them separately.
Where Distilled Water Still Makes Sense
Some devices call for distilled water, and some do not. The difference can come down to a single part on the same machine:
- CPAP machine humidifiers: ResMed specifies distilled water only for its HumidAir 11 Standard water tub, but drinking-quality water for its HumidAir 11 Cleanable tub.
- Steam irons: Philips states in its steam iron manuals that the irons are designed for tap water, and in hard-water areas it suggests distilled or demineralized water, or a 50/50 mix with tap water.
- Room humidifiers: The EPA recommends low-mineral water, such as distilled water, in humidifiers, especially ultrasonic and impeller types, and regular cleaning still matters.
Follow the instructions for your exact model rather than substituting RO water because it seems close enough. For these small volumes, purchased distilled water is often simpler than running a distiller. Distilled water, whether made at home or bought by the jug, is not the same as the sterile water used for medical purposes.
Which One Fits Your Kitchen
For most kitchens, the reverse osmosis vs distilled water choice comes down to volume and hands-on time:
- Reverse osmosis system: fits households that want drinking, cooking, and ice water on tap without batching or buying jugs.
- Countertop distiller: fits households comfortable with batch timing, electricity use, and descaling, or where installing RO is not practical.
- Purchased distilled water: fits small device needs where the manual calls for distilled water.
If convenience is what decides it for you, our guide to choosing an RO system for your home walks through sizing and features. We offer Thirst RO Pure, Restore, and Thrive systems, including options with remineralization. You can compare our reverse osmosis systems and ask our team which model fits your water and taste preferences.
Frequently Asked Questions
Can I use RO water instead of distilled water in a CPAP?
Only if your device’s manual allows it. Requirements can differ even between two water tubs on the same machine, so follow the instructions for your exact tub and device. When the manual says distilled water, use distilled water rather than treating RO water as an equal substitute.
Is purified water the same as distilled water?
Not necessarily. Under U.S. bottled-water rules, purified water can be made by distillation, reverse osmosis, deionization, or another suitable process that meets the purity definition. A “purified” label alone does not tell you which process was used, so look for “distilled” on the label if a device calls for it.
Does a water softener help an RO system or a distiller?
It can, depending on your water and equipment. A softener reduces the hardness minerals that cause scale in both, but it does not lower total dissolved solids, so it supports either method rather than replacing it. A water test shows whether pretreatment makes sense for your home.
Is boiled water the same as distilled water?
No. Boiling heats water in the same pot, so the dissolved minerals stay in the water you drink. Distillation boils water, captures the steam, and condenses it into a separate container, which leaves most minerals behind in the boiling chamber. The two produce very different water, even though both involve heat.
Start With Your Water
For a steady supply at the kitchen tap, choose RO; a distiller works if its batch output and upkeep suit your household; and purchased distilled water covers devices whose manual calls for it. The right setup depends on what is actually in your home’s water, which city ranges cannot show. A good first step is testing your tap water, or you can book a free in-home water test from Clear Water Concepts that checks hardness, TDS, and chlorine. From there, our team can help you choose a reverse osmosis system that fits your Mesa, Glendale, and Tucson home’s water and daily use.
