Reverse osmosis is the most comprehensive residential and commercial water purification technology available. A properly designed RO system forces pressurized water through a semi-permeable membrane with pores small enough to block dissolved salts, heavy metals, and organic compounds while allowing water molecules to pass. The result is purified water with 95-99% rejection of total dissolved solids. Here are the 10 most important contaminants that RO systems remove, along with the data on removal rates and why each matters.
1. Lead
Typical RO removal rate: 97-99%
Lead enters drinking water from lead service lines and plumbing solder in buildings constructed before 1986. There is no established safe level of lead in drinking water for children. RO membranes certified to NSF/ANSI Standard 58 for lead reduction are the most reliable point-of-use protection available.
2. Arsenic
Typical RO removal rate: 92-96%
Arsenic occurs naturally in groundwater across the western United States, New England, and the Midwest. Long-term exposure to arsenic above the EPA Maximum Contaminant Level of 10 ppb is associated with skin, bladder, and lung cancers. Carbon filters and water softeners do not remove arsenic. RO is the most widely recommended point-of-use technology for arsenic reduction.
3. Fluoride
Typical RO removal rate: 85-92%
Municipal water is fluoridated at 0.7 ppm to support dental health. Some households prefer to reduce their fluoride intake for personal health reasons. Carbon filters do not remove fluoride; RO is the appropriate residential technology for fluoride reduction.
4. Nitrates
Typical RO removal rate: 83-92%
Nitrates from agricultural fertilizers, septic systems, and animal waste enter groundwater and surface water supplies. The EPA MCL for nitrates is 10 mg/L. Above this level, nitrates cause methemoglobinemia in infants under 6 months. RO is one of only a few point-of-use technologies capable of reducing nitrates to safe levels.
5. PFAS Compounds
Typical RO removal rate: 90-99%
Per- and polyfluoroalkyl substances, including PFOA, PFOS, and related compounds, have contaminated water supplies near military bases, airports, and manufacturing sites across the US. In 2024, the EPA finalized the first federal MCLs for PFAS at 4 parts per trillion. RO membranes reject PFAS at rates of 90-99%, making them the most effective residential barrier against these compounds.
6. Chlorine and Chloramines
Typical RO removal rate: 98-99% via carbon pre-filter stage
Chlorine and chloramines are added by utilities as disinfectants but create trihalomethanes and haloacetic acids as byproducts when they react with organic matter. A multi-stage RO system with a carbon pre-filter removes both the primary disinfectants and their byproducts.
7. Chromium-6
Typical RO removal rate: 85-95%
Hexavalent chromium is an industrial contaminant that entered public consciousness via the Hinkley, California groundwater contamination case. It is a confirmed human carcinogen at elevated concentrations. RO is one of the few point-of-use technologies that provides meaningful chromium-6 reduction.
8. Bacteria and Viruses
Typical RO removal rate: 99.9% for bacteria; 99%+ for viruses with UV post-treatment
RO membranes have pores approximately 0.0001 microns in size, small enough to physically block bacteria and most viruses. Point-of-use RO with UV post-treatment provides microbiological protection during boil-water events for common contamination scenarios.
9. Total Dissolved Solids
Typical RO removal rate: 95-99%
TDS is the aggregate measure of dissolved minerals, salts, and metals in water. RO reduces TDS to levels below 50 ppm from source water TDS of 300-1,000 ppm in typical municipal applications. Low TDS output improves taste and reduces scale buildup in appliances.
10. Pesticides and Herbicides
Typical RO removal rate: 95-99%
Agricultural runoff introduces atrazine, simazine, and other regulated pesticides into surface water sources. RO membranes reject most organic pesticides and herbicides at rates exceeding 95%, providing consistent protection independent of source water variability.
Choosing a Certified RO System
When evaluating a system, look for NSF/ANSI certification under Standard 58, which verifies contaminant reduction claims through independent testing. AMPAC USA residential and commercial RO systems use NSF-certified components. Contact AMPAC USA to discuss which system fits your application.
Frequently Asked Questions
Does RO remove all contaminants?
RO removes the vast majority of dissolved contaminants, but no single technology removes everything. Radon, some dissolved gases, and certain low-molecular-weight organic compounds may pass through at reduced levels. A carbon pre-filter and UV post-treatment address most gaps in RO-only systems.
Does RO remove beneficial minerals?
Yes. RO removes calcium, magnesium, potassium, and other dissolved minerals along with contaminants. This is generally not a health concern as dietary mineral intake from food far exceeds what drinking water provides. Post-RO mineral filters can add calcium and magnesium back to the permeate if desired.
Sources: EPA Drinking Water Regulations | NSF International | Water Quality Association | EPA PFAS