Water filters · point of use

Reverse Osmosis Systems

An RO system pushes water through a membrane that rejects most dissolved solids and sends the rest to a drain. What an exact unit is certified to reduce, how much water it sends to the drain, and what it costs to keep running differ model to model.

A membrane rejects dissolved solids and sends the rest to a drain. What each exact unit is certified to reduce, and costs to run, differs.

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How reverse osmosis worksHow RO worksTreats 1 outlet · needs a drainNeeds a drain

What it does

A membrane, not a filter.

Pressure forces water through a membrane fine enough to reject dissolved solids, including lead, arsenic, nitrate, fluoride and most of the TDS reading. What doesn’t pass goes to the drain, so every RO needs a drain connection and sends some water down it for each gallon it makes.Pressure forces water through a membrane fine enough to reject lead, arsenic, nitrate and most TDS. What doesn’t pass goes to the drain.

Who it suitsAnyone whose water carries dissolved contaminants a carbon filter won’t touchWater with dissolved contaminants carbon won’t touch
What it needsA drain, the maker’s minimum inlet pressure, and cabinet depth for a tankA drain, the minimum inlet pressure, cabinet depth for a tank
What it won’t doTreat the shower, or make up for low pressureTreat the shower, or fix low pressure
Running costCartridges and a membrane on the maker’s schedule, plus drain water

WaterDecoder’s picks · from systems in our database that qualify for this job · not a ranking

Our picks

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Our editors haven’t curated reverse osmosis picks yet.

There are no picks for this set yet. Every system in our database is in the catalogue below, and Finder can match one to your home.

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Picks are editorial and the table is a list. Neither knows your water, your pressure or your cabinet. Tell Finder what you want in your own words. It asks only what it needs, then matches exact configurations. It may still recommend a different type once it knows your water.

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The catalogue

All RO systems, side by side

No published products

No published products in this category yet.

We don’t have any reverse osmosis in our database yet. When one is added with its evidence on file, it appears here with its basis and the facts that decide a purchase.

Under-sink carbon · no drain, no membrane →Countertop RO · no plumbing →Hard water? Water softeners →

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Before you buy

Four numbers decide an RO before the brand does.

Drain ratio: Ratiodrain to treated; Gallons to drain for every gallon treated. A 2 : 1 unit sends half as much water to the drain as a 4 : 1, and that shows on your water bill.Gallons to drain per gallon treated. 2 : 1 sends half as much to drain as 4 : 1.
Inlet pressure: Minimuminlet pressure; Membranes need a minimum inlet pressure to reach rated output, and the maker states it. Tankless units are the most sensitive; a pressure gauge tells you where you stand.Membranes need a minimum pressure, stated by the maker. Tankless units are the most sensitive.
Rated throughput: Ratedat test conditions; A figure measured at the maker’s stated test conditions. Real output falls with lower pressure and colder water. It is a ceiling, not a promise.A figure at stated test conditions. Real output falls with pressure and temperature.
Consumables: Replacedon a schedule; Cartridges are replaced regularly and the membrane less often; the maker states each interval. Fewer, non-proprietary parts are the cheapest kind of ownership.Cartridges are replaced regularly, the membrane less often.

Also decidesTarget-by-target claimsWhich contaminants are certified, by what basis, for which membrane and cartridge. Never a blanket claim like “99% of everything”.Tank or tanklessCabinet depth and instant flow versus a pump and a power outlet under the sink.PowerBooster pumps and tankless designs need an outlet. Many cabinets don’t have one.Six-year ownershipPurchase plus consumables plus drain water, shown only where we hold every input.