Reverse osmosis drinking water systems, chosen for what your water actually has

What reverse osmosis is

A reverse osmosis system uses pressure to force water through a semi-permeable membrane, and most systems add filters before and after the membrane.^[source] A typical home unit has a sediment pre-filter, carbon to protect the membrane and handle taste, the membrane itself, and a final carbon polishing filter. Treated water goes to a storage tank or straight to a dedicated faucet; rejected water carries what the membrane held back to the drain.

Almost all home RO is point-of-use: it treats the kitchen tap where you drink and cook. Whole-house RO exists but is rarely the right tool for a home.

Who it's for

On city water

Municipal water here meets its standards; Charlotte Water reported zero violations for 2025.^[source] City-water households choose RO for taste, to cut bottled-water use, to reduce PFOA/PFOS where their utility reports them, or because a tap test found lead from their own plumbing. Our city-water RO page covers that case in detail, and the PFAS filtration page lists local utility results.

On a private well

Wells are where RO most often solves a specific, measured problem. Arsenic is the common one locally. Among private wells tested in Union County, 19.46% of 5,154 were above the 10 µg/L federal arsenic standard.^[source] In Stanly County, 18% of 1,278 tested wells were above it.^[source] Those figures describe wells that were tested, not every well, and the only way to know about yours is a certified-lab well test. See our well-water arsenic guide for the full picture.

Reading NSF/ANSI 58 the right way

NSF/ANSI 58 is the standard for reverse osmosis drinking water systems.^[source] Certification is per contaminant and per model: each certified system's listing names the exact claims it earned, such as Arsenic (Pentavalent), Lead Reduction, Nitrate/Nitrite Reduction or TDS Reduction.^[source] A system isn't certified for anything that isn't on its listing.

• Arsenic: the claim is for pentavalent arsenic, and listings note the product is intended only for water at or below the tested concentration and form of arsenic.^[source] Well water can carry arsenic in another form, so a lab result and sometimes a pre-treatment step matter before you rely on RO alone.
• PFAS: EPA advises looking for certification under NSF/ANSI 53 or 58 that covers the specific PFAS you want to reduce.^[source]
• Lead: look for a Lead Reduction claim on the model's listing.^[source]
• TDS: RO is very good at lowering total dissolved solids. A TDS meter shows that; it does not show whether your water was contaminated before.

What RO doesn't do

• It doesn't treat your showers, laundry or water heater. For those, see whole-home filtration or well treatment.
• It doesn't soften your house. Hardness scale needs a softener, and only when a test shows hard water; see water softeners.
• It isn't a fix for a well with bacteria. That starts with finding the cause, then disinfection; see UV disinfection.
• Heavy iron, manganese or hardness can foul a membrane early, so on wells those are treated first.

Things to weigh

• Drain water: EPA notes household RO can send about one gallon to the drain for each gallon treated.^[source] EPA WaterSense-labeled RO systems must be certified to NSF/ANSI 58, include an automatic shut-off and have an efficiency rating of at least 30 percent.^[source] On a septic system, factor in that extra flow.
• Remineralization: some systems add minerals back after the membrane. That's a taste choice. We don't make health claims for it, and you should be wary of anyone who does.
• Space and faucet: the tank and housings need cabinet space, and you'll usually need a faucet hole.
• Water pressure: RO depends on pressure; low-pressure wells sometimes need a booster pump.

How we approach it

1. Step 1

   Start with data

   Your utility's report for city water, or a certified-lab panel for a well. No in-home color demos.

2. Step 2

   Match the certification to the goal

   We look for systems whose NSF listing covers your actual contaminant, at your water's levels.

3. Step 3

   Plan pre-treatment if needed

   On wells, iron, manganese or hardness may need handling first so the membrane lasts.

4. Step 4

   Install and retest

   A licensed independent plumber installs it; a follow-up test confirms what's coming out of the tap.

Under-sink RO connects to your cold-water line and drain, which is licensed plumbing work. Here's how installation is handled.

Maintenance schedule

EPA notes that RO requires changing filter cartridges and the membrane, and that filters only perform if maintained on the manufacturer's schedule.^[source] Expect three categories of change:

• Pre-filters (sediment and carbon): the most frequent change, because they protect the membrane from grit and chlorine.
• Post-filter: a less frequent change for final taste polishing.
• Membrane: the least frequent change, sooner on harder or dirtier water.

Exact intervals depend on the model and your water. A Care Plan schedules the changes and includes a retest so you know the system is still meeting its claims.