Reverse osmosis (RO) is widely regarded as one of the most effective technologies for removing per- and polyfluoroalkyl substances (PFAS) from drinking water. By forcing water through a semi-permeable membrane with pores small enough to block PFAS molecules, RO systems can achieve removal rates of 90% or higher for compounds like PFOA and PFOS.
How the Membrane Works
A standard RO membrane has a pore size of approximately 0.0001 microns — far smaller than most PFAS molecules, which range from 0.0009 to 0.001 microns in size. This size exclusion mechanism physically prevents PFAS from passing through, capturing them in the reject stream that is flushed away during operation.
Unlike activated carbon, which relies on chemical adsorption and can become saturated over time, RO membranes maintain consistent performance until the membrane itself degrades. Most high-quality RO membranes last 2 to 5 years under normal residential use.
Whole-House vs. Point-of-Use RO
Point-of-use RO systems installed under the sink or on the countertop protect drinking and cooking water at a single tap. These systems are cost-effective and easy to maintain. Whole-house RO systems treat all water entering the home, which is valuable in areas with severe PFAS contamination but comes with higher installation and operating costs.
For most households, a point-of-use RO system paired with pre-filters provides excellent PFAS protection at a manageable price point. Look for systems certified to NSF/ANSI 58 for verified PFAS reduction performance.
Limitations to Consider
RO systems produce a reject stream containing concentrated contaminants, typically 2 to 4 gallons of wastewater per gallon of purified water. Additionally, RO removes beneficial minerals alongside contaminants, and some systems include a remineralization stage to restore calcium and magnesium for better taste and health benefits.