Reverse Osmosis Filtration
Reverse osmosis (RO) is the most comprehensive point-of-use water treatment technology available for residential use. It removes 90–99% of dissolved contaminants including PFAS, lead, arsenic, nitrates, and disinfection byproducts by forcing water through a semi-permeable membrane with pores of approximately 0.0001 microns.
What It Does
Reverse osmosis works by applying pressure to push water across a semi-permeable membrane that blocks dissolved salts, metals, chemicals, and most contaminants while allowing water molecules to pass through. A standard under-sink RO system includes a pre-sediment filter, a carbon pre-filter, the RO membrane, a post-carbon polishing filter, and a storage tank. Systems typically reject 3–4 gallons of water for every gallon of purified water produced.
What It Does and Doesn't Solve
Effectively Addresses
PFAS / PFOA / PFOS — 90–99% removal (NSF/ANSI 58 certified systems)
Lead — 95–99% removal
Arsenic — 90–95% removal
Nitrates — 85–95% removal
Total dissolved solids (TDS) — 90–95% reduction
Disinfection byproducts (TTHMs, HAA5) — 90%+ removal
Fluoride — 85–95% removal
Chromium-6 — 80–90% removal
Chlorine and chloramine taste/odor
Does Not Address
Does not treat the whole house — only the connected tap
Not certified as a primary disinfection method — bacteria and viruses require UV or boil-water treatment for reliable removal
Does not remove dissolved gases (radon, hydrogen sulfide)
Does not soften water (hardness minerals largely removed but purpose-specific softener is different)
Reduces but does not eliminate all volatile organic compounds (VOCs) — carbon pre-filter handles most
Wastes 3–4 gallons of water per gallon of purified water (some systems are more efficient)
Best For
Households with multiple contaminant concerns, PFAS or nitrate issues, or anyone wanting the broadest possible reduction in drinking water contaminants. Also the right choice when you want a single solution verified to address your specific water test results.
Cost & Maintenance
Cost Range
$200–$600 for the unit; $50–$150/year for replacement filters. Professional installation adds $150–$300.
Maintenance
Pre-filters (sediment and carbon): replace every 6–12 months. RO membrane: replace every 2–5 years depending on water quality and usage. Post-carbon filter: replace annually. Total annual filter cost typically $50–$150. Some systems have filter replacement indicator lights.
Installation Type
Standard under-sink installation requires 2–4 hours for a DIY-capable homeowner or a plumber. Requires a cold water supply line connection, a drain connection, and a small hole drilled in the sink or countertop for the dedicated faucet. No electrical connection needed for gravity-fed systems; some models have booster pumps requiring a power outlet.
Contaminants Addressed by Reverse Osmosis
PFAS
high risk · Synthetic Chemicals
Lead
high risk · Heavy Metals
Nitrates
moderate risk · Agricultural Chemicals
DBPs
moderate risk · Disinfection Byproducts
Arsenic
moderate risk · Heavy Metals
Chlorine
low risk · Disinfection Chemicals
Microplastics
moderate risk · Emerging Contaminants
Bacteria
high risk · Microbial Contamination
Fluoride
low risk · Minerals
Chromium-6
high risk · Heavy Metals
Copper
moderate risk · Heavy Metals
Iron & Manganese
low risk · Minerals
Uranium
moderate risk · Radioactive Contaminants
Perchlorate
moderate risk · Industrial Chemicals
VOCs
high risk · Industrial Chemicals
Radium
moderate risk · Radioactive Contaminants
Crypto & Giardia
high risk · Microbial Contamination
Selenium
low risk · Minerals
Cadmium
moderate risk · Heavy Metals
Mercury
moderate risk · Heavy Metals
Barium
low risk · Heavy Metals
Frequently Asked Questions
Testing and Treatment Path
Look up your utility's EPA compliance record
Search by ZIP code or utility name — violations, PFAS, and official sources
Official PFAS monitoring records (EPA UCMR 5)
Search which utilities have PFAS above the minimum reporting level
Find a certified water testing lab
State-certified labs for PFAS (Method 533/537.1), lead, nitrate, and bacteria
PFAS contamination records and watchlist
EPA limits, health context, utility violations, and removal methods
Lead violations and utility compliance records
EPA limits, health context, utility violations, and removal methods
Nitrate violations and well water guidance
EPA limits, health context, utility violations, and removal methods
Data sources and methodology
How EPA SDWIS, UCMR 5, and CCR data is sourced and displayed
Common Questions About Reverse Osmosis Filtration
What contaminants does Reverse Osmosis remove?
Removes: PFAS, Lead, Nitrates
Where can I test my water before choosing a filter?
State-certified labs for PFAS, lead, nitrate, and bacteria — confirm what's in your water first
Which utilities have open violations requiring treatment?
Search for EPA compliance records by ZIP code or utility name
Is there PFAS in my water system?
Official EPA UCMR 5 PFAS monitoring records by utility and compound
How is treatment effectiveness data sourced here?
NSF certification, EPA treatment guides, and WQA data — sources and accuracy notes
Related Pages
Per- and Polyfluoroalkyl Substances (PFAS)
Synthetic Chemicals
Lead in Drinking Water
Heavy Metals
Nitrates in Drinking Water
Agricultural Chemicals
Disinfection Byproducts (DBPs)
Disinfection Byproducts
Arsenic in Drinking Water
Heavy Metals
Chlorine & Chloramine in Drinking Water
Disinfection Chemicals
Microplastics in Drinking Water
Emerging Contaminants
Bacteria & E. Coli in Drinking Water
Microbial Contamination
Fluoride in Drinking Water
Minerals
Chromium-6 (Hexavalent Chromium) in Drinking Water
Heavy Metals
Copper in Drinking Water
Heavy Metals
Iron & Manganese in Well Water
Minerals
Uranium in Drinking Water
Radioactive Contaminants
Perchlorate in Drinking Water
Industrial Chemicals
Volatile Organic Compounds (VOCs) in Drinking Water
Industrial Chemicals
Radium in Drinking Water
Radioactive Contaminants
Cryptosporidium & Giardia in Drinking Water
Microbial Contamination
Selenium in Drinking Water
Minerals
Cadmium in Drinking Water
Heavy Metals
Mercury in Drinking Water
Heavy Metals
Barium in Drinking Water
Heavy Metals
Activated Carbon Filtration
Whole-home
Water Softener (Ion Exchange)
Whole-home
UV Water Purification
Under-sink
Data Sources & Provenance
All data on this page is sourced from official U.S. government or public datasets.
At a Glance
Type
Point-of-Use (Under-sink or Countertop)
Cost Range
$200–$600 for the unit; $50–$150/year for replacement filters
Contaminants Addressed
9 known
NSF/ANSI Certification
Always verify that a specific filter product is certified by NSF International or the Water Quality Association (WQA) for the contaminants you are targeting. Brand names alone do not guarantee effectiveness.
Other Treatment Methods