Start with your finding, not a product
A filter that is excellent for hard water may do nothing for PFAS, and vice versa. Before you buy, open your city water report so you know which contaminants are actually on the record — and if it matters for your home, run a test of your own tap. Then match the technology to the concern.
Most RO certifications cover arsenic V. Arsenic III, found in some wells, is reduced less well unless it is oxidized first, so if your well has arsenic, ask a water treatment professional about testing its form or pre-treatment.
PFAS: certified reverse osmosis or certified carbon
For PFOA and PFOS, choose a certified reverse osmosis (RO) system or an activated-carbon block certified for PFOA and PFOS. EPA also lists ion exchange. RO covers more contaminants; a certified under-sink or countertop unit handles a household's drinking and cooking water. Look for NSF/ANSI certification that names PFOA and PFOS, not a generic 'purifier' claim.
EPA's home-filter guidance, as of April 2024, says certifications focus on PFOA and PFOS and do not yet show a filter reaches EPA's 2024 limits, though reducing PFAS still limits your exposure. Some listings show a combined Total PFAS claim, which doesn't establish any one compound, so check that the listing names the compound in your result. A listing may not cover PFHxS, PFNA or GenX.
Lead: NSF/ANSI 53 certified
For lead, the key is the certification, not the format. A faucet or pitcher filter certified to NSF/ANSI 53 for lead reduction is a low-cost, no-plumbing option; an RO system certified for lead reduces it as well. Confirm the specific model's listing before buying, and see reading a lead result on your report for context.
Arsenic and nitrate: certified reverse osmosis
For arsenic and nitrate — common in some groundwater and agricultural areas — reverse osmosis certified for that contaminant is the most accessible point-of-use option; other filters may also work when the listing names it. These are worth prioritizing if you are on a private well, which federal monitoring does not cover.
Hard water: a softener, built for hardness
Hardness is an aesthetic and plumbing matter, not a health contaminant, and is excluded from the health-based Purity Score. An ion-exchange softener addresses hardness, scale and soap performance. A salt-free conditioner reduces scale, not hardness. Neither is built for lead, PFAS or germs. See do you need a water softener for the decision.
One honest caveat
Certified lab performance assumes correct installation and timely cartridge changes. A filter past its rated capacity can stop working. Set a replacement reminder the day you install it, and re-test to confirm it is doing the job. PurityMap may earn an affiliate commission on some product links, at no cost to you.
This article gives general guidance on treatment technology. It is not medical advice and does not determine whether any water is fit for a specific person. For health concerns about a specific contaminant, consult a licensed healthcare professional, and use a certified laboratory to test your own water.