# Reverse Osmosis Membrane Performance: What RO Actually Removes > RO semi-permeable membranes reject many dissolved ions and molecules when pressure, recovery, and membrane integrity are right—maintenance decides real-world results. *Published 2026-07-10 · Updated 2026-07-10 · By Elena Voss* In short RO works by **pressure-driven membrane rejection** of many dissolved contaminants. **NSF/ANSI 58 claims**, prefilters, integrity, and maintenance decide whether kitchen water matches brochure curves. *This article is informational and editorial only. It is not medical advice, diagnosis, or a treatment plan. Numbers and literature ranges cited here are not personal prescriptions. Consult a qualified clinician before changing medications, supplements, diet, equipment, or management of a diagnosed condition. Seek urgent care for emergencies.* ## How does RO membrane rejection work? A semi-permeable membrane allows water to pass while rejecting a high fraction of dissolved ions and many larger molecules under pressure. Rejection percentages differ by ion charge, size, membrane chemistry, temperature, and recovery. Manufacturers publish curves; field water differs from lab water. That is why certification to stated contaminants matters more than internet TDS bragging. [NSF/ANSI 58](https://www.nsf.org/consumer-resources/articles/standards-water-treatment-systems) is the consumer RO standard frame. [EPA](https://www.epa.gov/sciencematters/reducing-pfas-drinking-water-treatment-technologies) lists RO among PFAS-capable treatments when designed and maintained for that use. [EPA filter fact sheets](https://www.epa.gov/system/files/documents/2024-04/water-filter-fact-sheet.pdf) help households compare options. Performance factorWhy it mattersUser checkMembrane type/conditionCore rejectionTDS ratio; lab retest targetsPrefilter sediment/carbonStops fouling/chlorine damageChange on schedule or pressure dropFeed pressureDrives flux and rejectionGauge or installer checkRecovery/brine ratioWaste water and scalingKnow your system’s ratioPost-filter and tank hygieneTaste and recontaminationSanitize; replace post-filters ## What failure modes drop protection? Clogged prefilters that starve pressure, chlorine attack on thin-film membranes when carbon prefilters are exhausted, pinholes and O-ring leaks that blend reject and product water, biofilm in tanks, and ignored change schedules all produce false confidence. A system that once reduced arsenic can later fail silently without TDS or lab checks. ## How should remineralization and taste be handled? Some users add calcite or similar cartridges for taste and pH. That is optional relative to removing lead or nitrate. Mineral debate should not block treatment of documented hazards. For infant formula or low-mineral preferences, follow clinician guidance rather than internet mineralization dogma. ## When is RO the right tool versus not? Right: multi-contaminant wells, documented PFAS, nitrate, arsenic, or lead with appropriate certifications. Not first-line alone: untreated fecal contamination without disinfection plan, whole-house high-flow needs without commercial design, or homes with already excellent water chasing wellness TDS zero. Match tool to lab truth. Readers should treat this explainer as a map of mechanisms, measurements, and decision rules rather than a personal protocol. Local water quality, travel history, diet pattern, pregnancy status, occupational exposures, and baseline medical conditions change priorities week to week. When evidence grades are mixed, prefer certified products, clinician-directed testing, and primary agency sources over social media absolute claims. Revisit guidance as analytics, regulations, and clinical guidelines update, because measurement science and public-health standards continue to evolve. Practical exposure reduction and accurate terminology remain useful even when clinical dose-response curves are incomplete. Document your sources, test before you buy expensive gear, and keep food safety, infection control, and established medical care in the first tier of decisions. Secondary wellness products that promise detox, parasite purge, or total plastic elimination without diagnostic confirmation deserve skepticism proportional to their marketing intensity. For households, the highest-yield pattern is usually measure what matters, match a certified or clinically indicated control to the finding, and avoid stacking redundant gadgets that address the wrong contaminant class. For travelers and people planning pregnancy, timeline-sensitive risks such as infection, lead, nitrate, and heat deserve earlier attention than low-probability exotic hazards. For readers following nutrition debates, distinguish food-matrix fats from repeatedly heated industrial oils and from biomarker studies that do not measure fryer oxidation. Editorial standards on this site favor named organisms, named polymers, named filter certifications, and named study designs. Vague toxin language, unisex fertility scares without sex stratification, and silent unit conversions between mass and particle counts are treated as quality failures. Where human randomized evidence is thin, we say so and still offer proportionate precautions that do not require unproven supplements or extreme elimination diets. If you use this article alongside related Health Canon explainers, cross-check category hubs for water filtration, environmental health, hormones, and sex-specific pages so multi-route problems are not solved with a single product. Share decision-relevant lab results with a qualified clinician when symptoms, pregnancy, immunosuppression, or occupational exposures raise the stakes beyond general consumer guidance. Readers should treat this explainer as a map of mechanisms, measurements, and decision rules rather than a personal protocol. Local water quality, travel history, diet pattern, pregnancy status, occupational exposures, and baseline medical conditions change priorities week to week. When evidence grades are mixed, prefer certified products, clinician-directed testing, and primary agency sources over social media absolute claims. Revisit guidance as analytics, regulations, and clinical guidelines update, because measurement science and public-health standards continue to evolve. Practical exposure reduction and accurate terminology remain useful even when clinical dose-response curves are incomplete. Document your sources, test before you buy expensive gear, and keep food safety, infection control, and established medical care in the first tier of decisions. Secondary wellness products that promise detox, parasite purge, or total plastic elimination without diagnostic confirmation deserve skepticism proportional to their marketing intensity. ## Sources 1. [NSF standards](https://www.nsf.org/consumer-resources/articles/standards-water-treatment-systems) 2. [EPA PFAS treatment including RO](https://www.epa.gov/sciencematters/reducing-pfas-drinking-water-treatment-technologies) 3. [EPA water filter fact sheet](https://www.epa.gov/system/files/documents/2024-04/water-filter-fact-sheet.pdf) 4. [EPA NPDWR](https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations) --- Source: https://healthcanon.com/environmental-health/reverse-osmosis-membrane-performance Index: https://healthcanon.com/llms.txt · Full text: https://healthcanon.com/llms-full.txt