Reverse osmosis can reduce many dissolved salts, metals and other contaminants, but the exact answer depends on the complete system and its certified claims. The membrane is not a universal guarantee, and a generic list of substances cannot replace the certification record for the model you buy.
Most household systems also use sediment and carbon stages. Those stages can account for chlorine, taste and odour performance that the membrane alone does not provide.
What RO commonly reduces
| Substance or group | Typical answer | Important limit |
|---|---|---|
| Total dissolved solids | Yes | NSF/ANSI 58 requires a TDS-reduction claim; real performance varies with conditions |
| Calcium and magnesium | Yes | RO reduces hardness minerals at the drinking tap but is not a whole-house softener |
| Sodium | Often | Verify the model and rated conditions |
| Lead, arsenic, nitrate or fluoride | Some certified systems | Each requires the relevant product-specific claim |
| PFAS | Some certified systems | Look for the exact current claim and substances covered |
| Chlorine taste and odour | Usually through carbon | The membrane may be damaged by some disinfectants without pretreatment |
| VOCs | Often through carbon | RO alone is not the whole answer; check the VOC claim |
| Bacteria and viruses | Not a safe assumption | Many domestic units are intended for microbiologically safe feed water |
Certification matters more than the technology name
NSF describes NSF/ANSI 58 as the standard for point-of-use RO systems. Certification can include mandatory TDS reduction and optional claims for specific contaminants. A logo alone is not enough: confirm the model number and the claimed reduction in the certifier’s listing.
Use NSF’s contaminant-reduction claims guide or another accredited certifier’s database to match the device to your concern.
Does RO remove minerals?
Yes. RO reduces calcium, magnesium and many other dissolved ions. That can change taste and lower the mineral contribution from drinking water. Most people obtain minerals mainly from food, but treatment should still be selected for a real water-quality need rather than fear of all dissolved minerals.
If the goal is stopping scale throughout a home, a point-of-use RO tap is too narrow. See our guide to water-softener sizing.
Does RO remove bacteria and viruses?
An intact membrane can physically reject microorganisms, but ordinary domestic RO should not automatically be treated as a disinfection barrier. NSF’s scope for many point-of-use systems assumes water of known, microbiologically safe quality. Private wells and emergency supplies need risk-appropriate testing and treatment, potentially including validated disinfection.
What RO may not solve
- Aesthetic problems caused by the plumbing or water heater.
- Gases or very volatile compounds without appropriate carbon treatment.
- Microbial contamination when the system lacks a validated microbiological claim.
- Contamination introduced after the membrane in a dirty tank, faucet or tubing.
- Whole-house scale, staining or high flow demand when only one tap is treated.
How to verify a system
- Identify contaminants through the utility report or an accredited laboratory.
- Find the exact model in an independent certification database.
- Read every listed reduction claim and its test conditions.
- Check minimum pressure, feed-water limits, recovery and daily production.
- Maintain every stage on the documented schedule and retest where risk warrants it.
Before choosing equipment, compare the benefits and trade-offs of RO, alternative treatments and the EPA’s WaterSense RO guidance.
Bottom line
RO can reduce a broad range of dissolved contaminants, but only the exact model’s certified claims tell you what it is proven to reduce. Test first, match the claim and maintain the complete system.
