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
Frequently Asked Questions
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
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