Yes. Reverse osmosis removes most PFAS from Arizona tap water: EPA research found RO membranes typically more than 90 percent effective, including short-chain PFBS and PFBA, the two Phoenix detected at trace levels. Carbon holds those less well. Choose an under-sink unit certified to NSF/ANSI 58 for PFAS reduction and keep the membrane changed.
How does reverse osmosis remove PFAS?
Reverse osmosis (RO) pushes water under pressure through a very tight membrane. Clean water passes through; dissolved chemicals are held back and flushed to the drain. The EPA describes it as a process that "forces water through an extremely thin barrier that separates chemicals from the water."
PFAS dissolve in water, and the EPA notes that this is why traditional drinking water treatment is not able to remove them. Carbon works by holding chemicals on its surface, and some PFAS hold on better than others. A membrane separates them out instead, which fits the EPA's finding that RO handles shorter-chain PFAS too.
Most home units are three to five stage systems. The EPA's filter page describes RO as "typically a three, four, or five stage filtration process." Sediment and carbon prefilters protect the membrane, the membrane does the heavy lifting, and a polishing filter sits at the end. Our page on how a reverse osmosis install goes walks through where each stage sits under the sink.
Why short-chain PFAS matter for Phoenix homes
The EPA's fifth Unregulated Contaminant Monitoring Rule round covered 29 PFAS, and Phoenix monitored from January 2023 through January 2024. Its 2025 water quality report lists two PFAS detections:
| PFAS detected by Phoenix | Range | Average | Same range in parts per trillion |
|---|---|---|---|
| PFBS (perfluorobutanesulfonic acid) | 0.007 to 0.016 ppb | 0.011 ppb | 7 to 16 |
| PFBA (perfluorobutanoic acid) | 0.005 to 0.006 ppb | 0.005 ppb | 5 to 6 |
The report shows no MCL for either one, meaning neither has its own federal limit. The EPA's treatment research names both as shorter-chain PFAS. Now line that up with the EPA research: granular activated carbon "works well on longer-chain PFAS like PFOA and PFOS, but shorter chain PFAS like Perfluorobutanesulfonic acid (PFBS) and Perfluorobutyrate (PFBA) do not adsorb as well."
Here's the deal. A carbon filter is a fine choice for chlorine taste, and certified carbon can reduce PFOA and PFOS. But the specific PFAS that turned up in Phoenix testing are the ones carbon struggles with most. RO is the tool that covers them.
These numbers cover City of Phoenix water only. City reports do not cover private wells. The EPA's first step for anyone is to find out which PFAS, if any, are in your water, and it adds that if PFAS have not been measured, or are below federal limits, "a filter may not be useful to you." Well owners have no provider report to check, so a lab test is the only way to know. Our page on finding an Arizona-certified drinking water lab explains how to choose one.
For the city-by-city numbers, the federal limits and whether you need a PFAS filter at all, see our page on PFAS in Phoenix tap water. This page sticks to the RO question.
Does it have to be certified?
Yes, and the certification has to name PFAS. The EPA's advice is to check the packaging for certification to "NSF/ANSI 53" or "NSF/ANSI 58" for PFAS reduction. NSF/ANSI 58 is the reverse osmosis standard. A unit can carry a Standard 58 listing without a PFAS claim, so read the list of reduced contaminants, not just the standard number. The EPA says that if you are still in doubt, check the certification body's product directory.
Two honest limits from the EPA's pages:
- Claims focus on PFOA and PFOS. The EPA notes that as of April 2024, filter certifications focus on those two PFAS. If your concern is PFBS or PFBA, look in the product listing for those compounds by name. Our guide to checking a filter's certified claim shows how to read a listing.
- Certification is not a promise of the new federal limits. The EPA says the certification standards as of April 2024 "do not yet indicate that a filter will remove PFAS down to the levels EPA has now set for a drinking water standard."
Should it be under the sink or whole house?
Under the sink, for almost every home. The EPA research points the same way: because the membrane sends part of the water to drain as concentrate, it says "Perhaps this technology is best suited as a point of use technology for a homeowner."
You drink and cook with a few gallons a day. You do not need PFAS-treated water in the toilet tank or the irrigation line. A point-of-use RO system at the kitchen sink, with an extra line to the fridge if you like, covers the water that actually goes in your body.
Water use is the trade-off, and it counts in the desert. The EPA's filter page says a home RO system "Wastes about one gallon of water per every gallon treated." Efficiency varies by model, so compare the rated recovery before you buy. Our page on permeate pumps vs booster pumps covers the add-ons some systems use.
What keeps RO working on PFAS?
On-schedule maintenance keeps RO working on PFAS. The EPA says "Filters are only effective if they are maintained according to the manufacturer's instructions," and that missing the replacement schedule can increase your risk of exposure to PFAS. Stick to the maker's schedule rather than stretching it.
A few habits that help:
- Change prefilters on schedule. The carbon prefilter protects the membrane from chlorine.
- Replace the membrane at the interval the manufacturer lists for your model.
- Keep the paperwork. The model number is how you confirm the PFAS claim later.
Our RO filter replacement guide covers the full schedule.
An under-sink RO unit is a reasonable DIY job if you are comfortable tapping a cold line, drilling for a faucet and making a proper drain connection with an air gap. If you would rather have it done once and done right, HQ Plumbing & Air installs and services reverse osmosis systems through our water softening and filtration service. We give free estimates, and we're licensed and insured.