Reverse Osmosis vs Distilled Water: How They Are Made and Which Suits Which Job

Two different processes, reverse osmosis and distillation, land in a similar place: water with most of its dissolved minerals, metals and microorganisms taken out. They are not the same process, and the differences between them matter once you compare how much water and energy each one spends, how the treated water tastes, and which jobs around the house actually call for it. If you are weighing whether to keep buying jugs of distilled water or install a reverse osmosis system under the sink, it helps to look at both mechanisms first and then apply them to what you actually need the water for.

• Reverse osmosis pushes water through a semi-permeable membrane under pressure; distillation boils water and condenses the vapor that rises off it.
• Both processes strip out most dissolved minerals, which is generally why water from either one tastes flatter than tap or spring water.
• A home reverse osmosis system sends some water to the drain to keep the membrane working; distillation spends electricity boiling continuously instead.
• A live TDS reading, like the one on the RO600's display, shows how much is dissolved in a given glass. It does not by itself tell you whether the water is safe.

How Reverse Osmosis Actually Removes Impurities

A point-of-use reverse osmosis system works by pushing incoming water, under pressure, against a semi-permeable membrane whose pores are small enough to block dissolved solids, many metals and microorganisms while still letting water molecules through. The membrane divides the flow into two streams: a treated stream that continues on to your faucet, and a rejected stream that carries the blocked material away to the drain. The U.S. EPA's WaterSense program lists lead, PFAS, arsenic, bacteria and viruses among the contaminants a point-of-use RO system can remove (source: EPA WaterSense: Point-of-Use Reverse Osmosis Systems).

What "permeate" and "concentrate" mean

Picture the membrane as a very fine sieve held under constant pressure. Everything that makes it through on the clean side is called the permeate, and that is what fills your glass. Everything the membrane rejects, concentrated into a smaller volume of water, is the concentrate, and that stream has to go somewhere: down the drain. A multi-stage system such as the Hydrion Purity RO600 adds a sediment-and-carbon cartridge ahead of the membrane to catch larger particles and chlorine first, then a 0.0001-micron RO membrane, then a post-carbon and mineral stage that settles the taste before the water reaches the tap. For the full stage-by-stage mechanism, see our complete guide to reverse osmosis.

How Distillation Works: Boiling, Vapor and Condensation

Distillation takes a more direct route to a similar result. The unit heats water to boiling, and the water vapor that rises carries almost none of the dissolved minerals or solids with it. That vapor travels to a condenser, where it cools back into liquid, while most of what was dissolved in the original water stays behind in the boiling chamber as residue. The University of Nebraska-Lincoln Extension states that a properly operated home distillation unit can remove up to about 99.5% of impurities, including bacteria, metals, nitrate and dissolved solids (source: UNL Extension, NebGuide G1493: Drinking Water Treatment).

Distillation's boiling step separates on a different basis than reverse osmosis does: it depends on whether something travels with the water vapor at the boiling point, not on molecular size or electrical charge the way a membrane's pores do. Reverse osmosis works by pore size and pressure rather than by boiling point, so the two methods end up with different strengths depending on what is actually in your source water, and neither one is simply a stronger version of the other.

Where the Two Processes Differ: Water Use, Energy and Running Cost

The most honest way to compare the two day to day is by what each one spends to produce a litre of treated water. Reverse osmosis spends water: a typical home unit sends five or more gallons, sometimes up to ten, to the drain for every gallon of treated water it produces, which is why the EPA's WaterSense label caps certified units at 2.3 gallons to drain per gallon treated (source: EPA WaterSense). The RO600 runs at a 2:1 pure-to-drain ratio, meaning two parts treated water for every one part sent to the drain, which sits comfortably inside that WaterSense threshold. For the full math behind this figure, see our explanation of GPD and the pure-to-drain ratio.

Running a distiller spends electricity instead of water. Bringing a tank of water to a rolling boil and sustaining it takes continuous energy, and the same UNL Extension guidance that documents distillation's removal rate also flags its running cost as among the highest of home water-treatment options. At a larger scale, the same physics plays out: the U.S. Geological Survey notes that membrane-based reverse osmosis plants typically use less energy than thermal, distillation-type desalination, because moving water through a membrane under pressure is a different kind of work than boiling it (source: USGS: Reverse Osmosis Desalination). The trade-off at kitchen scale mirrors that pattern: an RO system costs you water, a distiller costs you electricity, and neither cost disappears just because the unit is small.

Why the Water Can Taste Different

Dissolved minerals make up a large part of what gives tap and spring water their characteristic taste, and both reverse osmosis and distillation remove most of them. That is generally why water from either process tastes flatter, or cleaner depending on your preference, than what comes out of the tap. Neither process is uniquely responsible for the effect; they arrive at a similarly low mineral content by different routes.

A live TDS, or total dissolved solids, reading, like the number shown on the RO600's display, tells you how much is dissolved in that particular glass right now. It is a useful way to confirm the system is working and to notice when a cartridge needs changing, but it is not a safety verdict on its own, and a lower number does not automatically mean the water is better suited to every use. For what the number actually measures and what a normal range looks like, see our explainer on TDS in water.

Should You Worry About Losing Minerals?

Both processes take out most of the calcium, magnesium and other minerals along with everything else they remove, and that raises a reasonable question: does drinking demineralized water matter for your health? The World Health Organization took the question seriously enough to convene a dedicated panel of nutrition, medical and scientific experts specifically to examine demineralized water and how it should optimally be remineralized (source: WHO: Nutrients in Drinking-Water). That the panel exists, and keeps being cited, says the question is treated as genuinely open among specialists rather than settled in either direction.

What is reasonably clear is that for most people eating a varied diet, drinking water is a minor source of calcium and magnesium next to food, so the mineral content of your drinking water alone rarely makes or breaks your intake. If you would rather address the question directly than keep weighing it, an inline remineralization stage such as the TAM3 alkaline mineral filter adds calcium, magnesium, potassium and zinc back after the RO stage and raises the pH above 7.5. For the mineral-by-mineral detail on what reverse osmosis removes and what survives, see our companion article on what reverse osmosis actually removes, and for the full how-to on adding minerals back, see why and how to remineralize RO water.

Which One Fits Your Situation: Drinking and Cooking vs. Small Appliances

For daily drinking and cooking, the practical difference comes down to logistics more than water chemistry. Buying and storing distilled water means repeat trips to the store and keeping jugs on hand, while an under-sink reverse osmosis system like the RO600 delivers treated water on demand at its own faucet, with a smart display that shows the live TDS of each glass as it fills.

For smaller, occasional uses, such as topping up a CPAP humidifier chamber, filling a steam iron or maintaining a battery, low-mineral water from either process generally limits scale buildup inside the device. The device's own manual remains the authority on which type of water it specifically calls for, since some manufacturers test and recommend one process over the other. For a broader look at where RO water helps and where it falls short, see our reverse osmosis benefits and drawbacks guide.

Weighed against each other, the two processes land in a similar place on water quality but differ clearly on what they cost to run: reverse osmosis trades some water for continuous on-demand output, while distillation trades electricity and time for a batch process that needs no plumbing. If the jugs of distilled water are the part you are tired of, an under-sink system is the direct substitute; if you only need small amounts occasionally, a countertop distiller or buying distilled water by the jug may still be the simpler choice.