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Sources and Standards

When we say an air purifier or water filter is “verified” or “certified,” we mean it appears in the official database of one of the organizations on this page. Here is what each one does, what its label actually proves, what it does not prove, and how you can check a product yourself in a couple of minutes.

Quick reference

OrganizationCategoryWhat it verifiesWhere to check
AHAM VerifideAirClean Air Delivery Rate (CADR) for smoke, dust, pollenAHAM Verifide directory
CARBAirOzone emissions at or below 0.050 ppm, plus electrical safetyCARB certified air cleaner list
UL 2998AirZero ozone emissions (validation)UL Product iQ / manufacturer certificate
ENERGY STARAirEnergy efficiency (smoke CADR per watt) and low standby powerENERGY STAR product finder
US Department of EnergyAirMinimum federal efficiency for air cleanersDOE compliance database
NSFWaterContaminant reduction and material safety to NSF/ANSI standardsNSF Listings
WQA Gold SealWaterCertification to NSF/ANSI and other standardsWQA Find Certified Products
IAPMO R&TWaterCertification to NSF/ANSI and other standardsIAPMO R&T listings
US EPABothDrinking water limits, indoor air guidance, ozone generator warningsepa.gov
CDC and WHOBothPublic health guidancecdc.gov, who.int

Air purifier standards

AHAM Verifide and CADR

The Association of Home Appliance Manufacturers (AHAM) runs a program that tests portable air cleaners under the AC-1 standard and reports Clean Air Delivery Rate, or CADR, in cubic feet per minute. Each certified unit gets three numbers: one for tobacco smoke (the smallest particles), one for dust, and one for pollen. Testing is done by an independent lab, and the results are listed in the AHAM Verifide directory.

What it proves: how quickly the purifier removes those particle types on its highest fan speed under standard lab conditions.

What it does not prove: performance on quieter fan speeds, odor or gas removal, or long-term filter performance.

How to use it. AHAM’s “two-thirds rule” says your purifier’s smoke CADR should be at least two-thirds of the room’s area in square feet (assuming an 8 ft ceiling). For wildfire smoke, AHAM suggests a CADR equal to the full room area.

Example: a 10 ft x 12 ft room is 120 sq ft (11.1 m²). You need a smoke CADR of at least 80 for everyday use, or 120 during wildfire smoke.

CARB (California Air Resources Board)

Ozone irritates the lungs, and some air cleaners (especially ionizers and ozone generators) release it. Since 2010, California has required portable indoor air cleaning devices sold in the state to be certified. Certified devices must emit no more than 0.050 parts per million (ppm) of ozone and meet an electrical safety standard such as UL 507 or UL 867. Since October 2020 the rule also covers electronic in-duct air cleaners.

What it proves: the device stays under California’s ozone emission limit and passed electrical safety testing.

What it does not prove: that the device cleans air well. A CARB-certified purifier can still have a low CADR.

How to check: search the model on CARB’s official list. Certified products can carry the label “Meets California ozone emissions limit: CARB certified.”

UL 2998 (zero ozone emissions)

UL 2998 is a separate validation from UL Solutions for products that produce effectively zero ozone. It is stricter than CARB’s limit. It is voluntary, so many good HEPA purifiers do not carry it.

EPA guidance on ozone generators

The US Environmental Protection Agency warns that ozone generators sold as air cleaners can produce ozone at levels that harm health and are not effective at removing most indoor pollutants. We do not recommend them.

ENERGY STAR and federal efficiency rules

ENERGY STAR, run by the EPA, certifies room air cleaners that meet efficiency requirements measured as smoke CADR per watt, along with limits on power used in standby. The current specification is Version 2.0, and ENERGY STAR notes a revision is in progress.

Separately, the US Department of Energy set mandatory federal efficiency standards for portable air cleaners. The first tier took effect December 31, 2023, and a stricter second tier took effect December 31, 2025. The DOE metric is PM2.5 CADR per watt.

What it proves: the unit is efficient for the air it cleans. What it does not prove: that it is powerful enough for your room.

HEPA definitions

“HEPA” is not a single worldwide certification.

  • US “True HEPA”: commonly refers to the Department of Energy definition of capturing at least 99.97% of particles 0.3 microns in diameter.
  • Europe, EN 1822: grades such as H13 (at least 99.95% at the most penetrating particle size) and H14 (at least 99.995%).
  • “HEPA-type,” “HEPA-like,” “99% HEPA”: no standard definition. Treat these as marketing terms.

A HEPA-grade filter only helps if air cannot leak around it, which is why we trust a verified CADR over a filter label.

Water filter standards

NSF International and the NSF/ANSI standards

NSF develops American National Standards for drinking water treatment and certifies products against them. Certification includes lab testing, material safety review, and ongoing facility audits. Most other water certifiers test to these same NSF/ANSI standards.

StandardCoversTypical claims
NSF/ANSI 42Aesthetic effectsChlorine, chloramine, taste and odor, particulates
NSF/ANSI 53Health effectsLead, cysts, certain VOCs, PFOA/PFOS, total PFAS
NSF/ANSI 58Reverse osmosisTDS, plus optional arsenic, nitrate, fluoride, PFAS and more
NSF/ANSI 55UV systemsClass A (disinfection) or Class B (supplemental)
NSF/ANSI 62DistillationContaminant reduction by distillers
NSF/ANSI 401Emerging contaminantsSelected pharmaceuticals, pesticides, other compounds
NSF/ANSI 372Lead-free materialsLow lead content in the product’s wetted parts (not reduction)
NSF/ANSI 177Shower filtersFree chlorine reduction

The most important rule: certification is contaminant-specific. A filter certified under NSF/ANSI 42 for chlorine is not certified for lead unless lead is listed under NSF/ANSI 53 for that exact model.

PFAS and the retired P473 protocol. NSF created Protocol P473 in 2016 to test filters for PFOA and PFOS. Those requirements were later incorporated into NSF/ANSI 53 and 58, which replaced P473. The standards were expanded in 2022 with a “total PFAS” claim that covers several PFAS compounds, and NSF has said its task groups are working to align the standards with EPA’s newer PFAS limits. If a product page still cites P473, check for a current NSF/ANSI 53 or 58 listing.

WQA Gold Seal

The Water Quality Association’s Gold Seal is the oldest third-party certification program in the water treatment industry. WQA is accredited by ANAB (US) and SCC (Canada) and certifies products to NSF/ANSI standards and others, with annual facility inspections.

How to check: search the WQA “Find Certified Products” directory.

IAPMO R&T

IAPMO Research and Testing is another accredited certifier that tests water treatment products to NSF/ANSI and related standards.

How to check: search IAPMO R&T’s online certification listings.

NSF vs WQA vs IAPMO: which is better?

For a buyer, a listing from any of the three accredited certifiers carries similar weight when it is to the same standard for the same contaminant. What matters is the specific standard, the contaminant, and whether the model number matches.

“Certified” vs “tested to standards”

“Tested to NSF/ANSI 53” means a lab ran a test using that method. It does not mean an accredited certifier reviewed the product, audits the factory, or re-tests it over time. It can still be useful if the brand publishes the full lab report, but it is not the same as certification, and we label it differently.

Drinking water regulations (EPA)

Safe Drinking Water Act limits

The EPA sets enforceable Maximum Contaminant Levels (MCLs) for public water systems, plus non-enforceable secondary standards for taste, odor, and appearance. Private wells are not regulated by the EPA, so well owners are responsible for their own testing.

Consumer Confidence Reports (CCRs)

Community water systems must send customers an annual water quality report. EPA revised the CCR rule in 2024 to make reports easier to read and to require twice-yearly reports for many systems, starting in 2027.

Lead

EPA’s health goal for lead in drinking water is zero. The Lead and Copper Rule Improvements, finalized in October 2024, lower the action level from 15 to 10 parts per billion and require most water systems to replace lead service lines within 10 years, with the main compliance date in November 2027. The rule has faced legal challenges, so we check EPA’s page for current status before citing dates.

PFAS

In April 2024, EPA set the first national drinking water limits for PFAS, including 4.0 parts per trillion each for PFOA and PFOS. In May 2026, EPA proposed keeping the PFOA and PFOS limits while extending the compliance deadline from 2029 to 2031, and proposed rescinding the limits for PFHxS, PFNA, GenX (HFPO-DA), and the mixture hazard index. As of our last check on September 17, 2026, those May 2026 proposals had not been finalized. We will update this section when they are.

Health and science sources

  • US EPA: indoor air quality guidance, the Guide to Air Cleaners in the Home, drinking water rules.
  • CDC: well water testing, wildfire smoke, mold, and asthma guidance.
  • WHO: global air quality guidelines and drinking water quality guidelines.
  • Peer-reviewed studies: we cite the journal and year, and we favor systematic reviews over single small studies.

Test and research benchmarks

We also read and cite independent testers who publish their methods, including HouseFresh for air purifiers and Water Filter Guru for water filters. We name them when we use their data, and we treat their results as independent data rather than certification.

Sources