What EPA says removes what — Best Available Technology, and what you can buy

By Andrew Bates, FounderPublished 2026-09-11Updated 2026-09-11

EPA publishes a legal list of what removes each regulated inorganic contaminant. Reverse osmosis appears on 12 of the 14 rows and ion exchange on 10. Granular activated carbon — the technology in most household filters — appears once, for mercury, and only below a stated influent level.

There is an official answer, and it is a regulation

Most “what removes what” advice online is somebody’s opinion. EPA’s version is in the Code of Federal Regulations.

Under 40 CFR §141.62(c), EPA identifies the “treatment technique, or other means available for achieving compliance” with each inorganic limit. The designation is Best Available Technology.

Thirteen technologies, fourteen contaminants, fluoride expressly excluded.

The ranking nobody publishes

Read down the technology column rather than the contaminant column and the picture changes.

Technology	Inorganics it is named for	Which ones
Reverse osmosis	12 of 14	All but asbestos and thallium
Ion exchange	10	Arsenic, barium, beryllium, cadmium, chromium, cyanide, nickel, nitrate, nitrite, thallium
Coagulation / filtration	8	Antimony, arsenic, asbestos, beryllium, cadmium, chromium, mercury, selenium
Lime softening	8	Arsenic, barium, beryllium, cadmium, chromium, mercury, nickel, selenium
Activated alumina	4	Arsenic, beryllium, selenium, thallium
Electrodialysis	4	Arsenic, barium, nitrate, selenium
Oxidation / filtration	1	Arsenic
Direct and diatomite filtration	1	Asbestos
Corrosion control	1	Asbestos
Alkaline chlorination	1	Cyanide
Granular activated carbon	1	Mercury, conditionally

Chlorine and ultraviolet appear in the key but on no inorganic row at all.

Carbon appears once

The technology inside most household filters is named for one inorganic contaminant.

That is mercury, and only “if influent Hg concentrations” are at or below 10 micrograms per litre.

This is not a criticism of carbon. It is a statement about what metals and dissolved salts do in the presence of carbon, which is mostly nothing.

→ Which claims exist at all, and how populated each is

Where carbon is the answer

The same regulation makes the opposite point a few paragraphs earlier.

For all six regulated PFAS entries — the Hazard Index mixture, HFPO-DA, PFHxS, PFNA, PFOA and PFOS — EPA names an identical set: anion exchange, GAC, reverse osmosis and nanofiltration.

Carbon’s domain is organic contaminants. Among inorganics it is a specialist tool for one metal under one condition.

→ PFAS: the six regulated compounds, and which have a claim

This explains the certification pattern

The site has recorded for months that fluoride, nitrate and hexavalent chromium are certified under NSF/ANSI 58 only, with no carbon claim anywhere.

EPA’s table is why. For nitrate it names ion exchange, reverse osmosis and electrodialysis. None of them is carbon.

The certification system is not being arbitrary. It is following the chemistry the regulation already describes.

→ Nitrate on city water

Naming a technology is not certifying a product

Worth stating plainly, because the two get conflated constantly.

EPA names nanofiltration for all six regulated PFAS. NSF offers no nanofiltration claim under any standard.

EPA names technologies at plant scale, with a utility’s budget and an operator on site. NSF tests a device against a stated challenge concentration in a laboratory.

A contaminant can have a named technology and no certified household product. 33 of EPA’s 94 regulated entries have no NSF claim at all.

→ The regulated contaminants with no certified filter

Every technology carries conditions

EPA does not name a technology unconditionally.

Contaminant	The condition
Mercury	BAT only if influent mercury is at or below 10 µg/L
Chromium	Lime softening is BAT for chromium III only
Selenium	Coagulation/filtration is BAT for selenium IV only
Arsenic	BATs are for arsenic V; pre-oxidation may be needed first
Arsenic	High removals need an iron to arsenic ratio of at least 20:1

Coagulation/filtration and lime softening are also not Best Available Technology for systems with fewer than 500 service connections.

This is the regulatory version of something this site keeps finding in NSF listings: performance is conditional on what arrives, not promised in the abstract.

→ Arsenic: the valency condition on every certified claim

The provision almost nobody knows

EPA allows a small water system to meet the arsenic limit using filters in customers’ homes.

Point-of-use activated alumina and point-of-use reverse osmosis are both listed as small system compliance technologies, affordable for all size categories, for systems serving 10,000 people or fewer.

With one condition. Where point-of-use or point-of-entry devices are used for compliance, “programs to ensure proper long-term operation, maintenance, and monitoring must be provided by the water system.”

So the same device counts as regulated treatment when a utility maintains it, and as an unmonitored purchase when you buy it yourself.

→ Once it is fitted: rated life, running cost, and the listed element

EPA concedes the water cost too

In the same table, on reverse osmosis and electrodialysis reversal:

“Technologies reject a large volume of water — may not be appropriate for areas where water quantity may be an issue.”

Which matches the household figure. Nebraska Extension puts domestic reverse osmosis recovery at 20 to 30 percent, and EPA elsewhere puts household units at roughly three times the water they treat.

→ Reverse osmosis: what NSF/ANSI 58 actually certifies

The decision framework

1. Find your contaminant’s named technology first

It tells you which family of product can possibly work, before any brand enters the conversation.

2. Check whether that technology exists in certified household form

Reverse osmosis and ion exchange do. Lime softening, coagulation and electrodialysis do not, at household scale.

3. Expect carbon to fail on metals and salts

One inorganic row in the whole table. If your problem is a metal other than mercury, or a dissolved salt, carbon is the wrong family.

4. Expect carbon to succeed on organics

It is one of four technologies EPA names for every regulated PFAS, and it handles chlorine taste and odour in thousands of certified models.

→ Chlorine and chloramine on city water

5. Read the condition, then read your own number

Valency, influent concentration, competing ions and pH all appear as conditions in this table. They appear in NSF claims for the same reasons.

The decision path

Your contaminant	EPA’s named technologies	Certified household form
Nitrate or nitrite	Ion exchange, RO, electrodialysis	RO only, 84 models
Arsenic	Seven, including activated alumina and RO	RO and carbon block, valency-conditional
Barium	Ion exchange, lime softening, RO, electrodialysis	Under NSF/ANSI 58, bundled
Chromium	Coagulation, ion exchange, lime softening, RO	RO for hexavalent, 120 models
Cadmium	Coagulation, ion exchange, lime softening, RO	Bundled in the NSF 58 set
Mercury	Coagulation, GAC, lime softening, RO	The one carbon-friendly inorganic
Asbestos	Coagulation, diatomite filtration, corrosion control	Certified claims exist under 53 and 58
PFAS	Anion exchange, GAC, RO, nanofiltration	GAC and RO; no nanofiltration claim
Thallium	Activated alumina, ion exchange	No NSF claim at all
Fluoride	Excluded from this table	RO only, 127 models

Choose reverse osmosis if

Your contaminant is one of the 12 inorganics EPA names it for, and a certified model holds the specific claim.
You need several inorganic claims at once, which the NSF/ANSI 58 bundle provides.

Choose carbon if

Your problem is organic: PFAS, disinfection byproducts, VOCs, or chlorine taste and odour.
You want the lowest-cost certified route to a claim carbon actually holds.

Choose neither if

Your contaminant’s named technologies are all plant-scale — lime softening, coagulation, electrodialysis — and no certified household product exists.

→ Which claims exist in which product form

Mistakes that cost the most money

Buying carbon for a metal. EPA names it for one inorganic in fourteen, and only below a stated influent level.

Reading a named technology as a purchasable product. Nanofiltration is Best Available Technology for PFAS and has no NSF claim at all.

Ignoring the condition. Arsenic technologies address arsenic V. Untreated arsenic III may pass a system designed on this table.

Assuming plant-scale means household-scale. Lime softening at a treatment works has no domestic equivalent.

Thinking a utility’s compliance choice is yours. When a utility uses point-of-use devices for compliance it must also run the maintenance and monitoring. You would be doing that yourself.

Treating this table as complete. It excludes fluoride and covers inorganics only. Organics are listed separately under §141.61.

Three situations, and what changes

A homeowner told a carbon block will fix high nitrate. EPA names ion exchange, reverse osmosis and electrodialysis for nitrate. Carbon appears nowhere on that row, and NSF offers no nitrate claim under either carbon standard. The claim being made is not supported by either system.

A small rural utility facing an arsenic exceedance. This is the case the small system table was written for. Point-of-use activated alumina or reverse osmosis in customers’ homes is a recognised compliance route for all size categories, provided the utility runs the operation and monitoring programme.

A household comparing a PFAS pitcher with a reverse osmosis system. Both technologies are named by EPA. The difference is certification depth: 72 models hold an NSF/ANSI 53 PFAS claim, of which one is a pitcher. The technology being correct does not make any given product certified.

The objections worth answering

“Carbon filters are the standard for a reason.” They are, for organics. EPA names GAC for all six regulated PFAS. Among the fourteen inorganics it is named once.

“This is just a government list, not real performance.” It is the list a utility must justify itself against when it fails a limit. It carries more consequence than any marketing claim.

“So reverse osmosis is the answer to everything.” It is named for 12 of 14 inorganics and no organics in that table, it rejects a large volume of water by EPA’s own note, and it is absent from every point-of-entry listing.

“If EPA names it, it must be available.” Nanofiltration for PFAS is named and uncertified. Thallium has two named technologies and no NSF claim at all.

“My filter says it reduces heavy metals.” Ask which metal and under which standard. EPA’s table treats mercury, cadmium, thallium and chromium as different problems with different technologies.

Who this is for

Anyone who wants the technology question answered before the product question, and anyone checking whether a claim made at the point of sale matches what the regulation says removes that contaminant.

It is also useful for understanding why the certified fields on this site are shaped as they are.

Utilities and operators will find the underlying table more authoritative than this summary of it.

What to settle first

Which technology does EPA name for my contaminant, and does that technology exist in a certified household product?

The first is in the regulation. The second is in NSF’s listing. A great many sales conversations end at the gap between them.

→ Which claims exist at all, and how populated each is → The regulated contaminants with no certified filter → How to check a certification claim yourself → Reverse osmosis: what NSF/ANSI 58 actually certifies → Which claims exist in which product form → Unregulated contaminants, where no limit and no claim exist → Radon: the technology EPA proposed and never required → Asbestos: the only inorganic with corrosion control as a technology

The bottom line

Read EPA's table as a ranking of technologies rather than a list of contaminants. Reverse osmosis and ion exchange carry almost the whole inorganic burden, which is why fluoride, nitrate and hexavalent chromium have no certified carbon product. Carbon's domain is organics, where EPA names it for all six regulated PFAS. And remember what the designation is not: naming a technology is not certifying a product, and EPA names nanofiltration for PFAS while NSF offers no nanofiltration claim at all.

Who this is not for

Best Available Technology is a plant-scale legal designation, not a shopping list. EPA is describing what a water system can use to meet a limit, with costs and scale it can bear. A household device using the same technology is a different product tested a different way, and the table excludes fluoride and covers inorganics only — organics are listed separately.

Questions

What is a Best Available Technology in drinking water?

A legal designation under 40 CFR §141.62, where EPA identifies the treatment technique or other means available for a public water system to achieve compliance with a maximum contaminant level. It describes plant-scale treatment, not household products.

Which technology does EPA name most often?

Reverse osmosis, listed for 12 of the 14 regulated inorganic contaminants other than fluoride. Ion exchange follows at 10, then coagulation and filtration and lime softening at 8 each. Activated alumina and electrodialysis appear 4 times each.

Is carbon filtration a Best Available Technology?

For inorganics, almost never. Granular activated carbon appears once in that table, for mercury, and only where influent mercury is at or below 10 micrograms per litre. For PFAS it is different: EPA names GAC for all six regulated PFAS entries.

Why can't a carbon filter be certified for nitrate or fluoride?

EPA names ion exchange, reverse osmosis and electrodialysis for nitrate, and none of them is carbon. NSF follows the same logic, offering nitrate and fluoride claims under NSF/ANSI 58 only and none under the carbon standards.

Can a utility meet a limit using filters in people's homes?

For arsenic, in small systems, yes. EPA lists point-of-use activated alumina and point-of-use reverse osmosis as compliance technologies, but the water system must provide programmes for long-term operation, maintenance and monitoring.

Does EPA naming a technology mean I can buy one?

No. EPA names nanofiltration for all six regulated PFAS, and NSF offers no nanofiltration claim under any standard. Best Available Technology and certified household performance are separate questions with separate answers.

Are the technologies always effective?

They carry conditions. Lime softening is Best Available Technology for chromium III only, coagulation and filtration for selenium IV only, and the arsenic technologies apply to arsenic V, possibly needing pre-oxidation first.

Does EPA acknowledge the water reverse osmosis wastes?

In the arsenic small system table it notes reverse osmosis and electrodialysis reversal reject a large volume of water and may not be appropriate where water quantity is an issue. Elsewhere EPA puts household units at roughly three times the water they treat.

Sources — 13 claims

40 CFR §141.62 — Maximum contaminant levels for inorganic contaminants (2024 edition, 40 CFR Ch. I, 7-1-24)
Under 40 CFR §141.62(c) EPA names thirteen Best Available Technologies for the fourteen regulated inorganic contaminants other than fluoride: activated alumina, coagulation/filtration, direct and diatomite filtration, granular activated carbon, ion exchange, lime softening, reverse osmosis, corrosion control, electrodialysis, chlorine, ultraviolet, oxidation/filtration and alkaline chlorination. (captured 2026-09-11)
Limits: Best available technology is a plant-scale judgement about what a public water system can use to meet a limit. Coagulation/filtration and lime softening are expressly not BAT for systems with fewer than 500 service connections. The table excludes fluoride, and organic contaminants are listed separately under §141.61.
40 CFR §141.62 — Maximum contaminant levels for inorganic contaminants (2024 edition, 40 CFR Ch. I, 7-1-24)
Reverse osmosis is the Best Available Technology EPA names most often for inorganic contaminants, appearing for 12 of the 14 listed, followed by ion exchange at 10 and lime softening at 8. Granular activated carbon appears exactly once, for mercury, and only where influent mercury is at or below 10 micrograms per litre. (captured 2026-09-11)
Limits: Counted across the inorganic table only. Granular activated carbon is separately named as a best available technology for all six regulated PFAS and is widely used for organic contaminants under §141.61, so its single appearance here bounds its role among inorganics rather than overall.
40 CFR §141.62 — Maximum contaminant levels for inorganic contaminants (2024 edition, 40 CFR Ch. I, 7-1-24)
EPA names four Best Available Technologies for every regulated PFAS entry — anion exchange, granular activated carbon, reverse osmosis and nanofiltration — applying the identical set to the Hazard Index mixture, HFPO-DA, PFHxS, PFNA, PFOA and PFOS. (captured 2026-09-11)
Limits: A plant-scale designation. NSF separately offers PFOA, PFOS and total PFAS reduction claims under NSF/ANSI 53 only, and offers no claim at all for HFPO-DA, so EPA naming a technology for a contaminant does not mean a certified household product exists for it.
40 CFR §141.62 — Maximum contaminant levels for inorganic contaminants (2024 edition, 40 CFR Ch. I, 7-1-24)
EPA lists point-of-use activated alumina and point-of-use reverse osmosis among the small system compliance technologies for arsenic, affordable for all size categories, and requires that where point-of-use or point-of-entry devices are used for compliance the water system must provide programmes for proper long-term operation, maintenance and monitoring to ensure adequate performance. (captured 2026-09-11)
Limits: This table is specific to arsenic and to systems serving 10,000 persons or fewer. A device in a customer's home counts toward a utility's compliance only where the utility runs the maintenance and monitoring programme; a household buying the same device privately carries that burden itself.
40 CFR §141.62 — Maximum contaminant levels for inorganic contaminants (2024 edition, 40 CFR Ch. I, 7-1-24)
EPA attaches conditions to several inorganic Best Available Technologies: granular activated carbon, coagulation/filtration and lime softening are BAT for mercury only where influent mercury is at or below 10 micrograms per litre; lime softening is BAT for chromium III only; coagulation/filtration is BAT for selenium IV only; and the arsenic technologies are for arsenic V, with pre-oxidation possibly required and an iron to arsenic ratio of at least 20 to 1 for high removals. (captured 2026-09-11)
Limits: The conditions are on the technology, not on the contaminant. A named technology that meets none of its stated conditions is not best available technology for that water, which is the regulatory analogue of a certified claim that is conditional on concentration and valency.
40 CFR §141.62 — Maximum contaminant levels for inorganic contaminants (2024 edition, 40 CFR Ch. I, 7-1-24)
EPA notes in the arsenic small system compliance table that reverse osmosis and electrodialysis reversal reject a large volume of water and may not be appropriate for areas where water quantity may be an issue, and that coagulation/filtration and lime softening are unlikely to be installed solely for arsenic removal. (captured 2026-09-11)
Limits: A plant-scale caution that matches the household one: Nebraska Extension puts household reverse osmosis recovery at 20 to 30 percent and EPA elsewhere states such units use approximately three times as much water as they treat.
EPA — Secondary Drinking Water Standards: Guidance for Nuisance Chemicals
EPA states corrosion control is perhaps the single most cost-effective method a public water system can use to treat for iron, copper and zinc, that coagulation and filtration remove metals such as iron, manganese and zinc, that aeration removes odours, iron and manganese, that granular activated carbon removes most of the contaminants causing odours, colour and foaming, and that distillation, reverse osmosis and electrodialysis are effective for chloride and total dissolved solids. (captured 2026-09-11)
Limits: Written as corrective actions a water supplier can take at plant scale, not as household product advice. EPA also states corrosion control is not used to remove metals from contaminated source waters, and that federal regulations do not require systems to monitor or treat for secondary contaminants at all.
EPA Office of Water — Home Water Treatment Facts / Filtration Facts (published November 2005)
EPA maps contaminants to home treatment technologies: Giardia and Cryptosporidium to distillation, reverse osmosis, absolute one micron filters, ultraviolet light and cyst-certified filters; bacteria and viruses to distillation, reverse osmosis, ultraviolet light and disinfection; arsenic to adsorptive media; lead to distillation, reverse osmosis and some carbon filters; nitrates to distillation, reverse osmosis or ion exchange; and radon to activated carbon and aeration. (captured 2026-09-10)
Limits: Technology classes, not product endorsements, from a 2005 EPA sheet. "Some carbon filters" for lead is EPA’s own hedge and should be read as requiring a certified lead claim on the specific model.
NSF Official Listings — Drinking Water Treatment Units, reduction-claim search (listings current as of Thursday, September 10, 2026, 12:15 a.m. Eastern Time)
Fluoride reduction, nitrate/nitrite reduction, TDS reduction and hexavalent chromium reduction are selectable in NSF’s listing search only under NSF/ANSI 58, and appear under neither NSF/ANSI 42 nor NSF/ANSI 53. (captured 2026-09-10)
Limits: A statement about which claims exist under which standard in NSF’s search, not about physics. It does not say a non-RO technology cannot reduce these, only that NSF/ANSI 42 and 53 offer no claim under which such a product could be certified for them.
NSF Official Listings — Drinking Water Treatment Units, NSF/ANSI 53 PFOA, PFOS and Total PFAS reduction-claim searches (listings current as of Thursday, September 10, 2026, 12:15 a.m. Eastern Time)
PFOA, PFOS and total PFAS reduction are selectable in NSF’s listing search under NSF/ANSI 53 only, and no PFAS claim appears under NSF/ANSI 58, although EPA advises looking for certification under NSF/ANSI 53 or NSF/ANSI 58 for PFAS reduction. (captured 2026-09-10)
Limits: A statement about which claims NSF offers, not about what reverse osmosis does. A system certified to NSF/ANSI 58 may also hold NSF/ANSI 53 certification separately, which is where any PFAS claim it carries would sit. The tension with EPA’s advice is reported, not resolved.
Crosswalk of EPA National Primary Drinking Water Regulations against the NSF reduction-claim taxonomy (both captured 2026-09-10)
Crossing EPA 94 regulated contaminant entries against NSF 101 selectable reduction claims on 2026-09-10 leaves 33 regulated contaminants with no NSF reduction claim of that name: 19 organic chemicals, 4 microorganisms, 4 inorganic chemicals, 3 disinfection byproducts and 3 radionuclides. (captured 2026-09-10)
Limits: The absence of a claim by name is not evidence that no product treats the contaminant. Reverse osmosis and distillation remove many of these; NSF offers no named claim to certify them against. NSF offers no claims at all under its distillation standard, so distillation is invisible to this crosswalk, and microorganisms are certified through NSF/ANSI 55 disinfection performance classes rather than by contaminant.
University of Nebraska–Lincoln Extension NebGuide G1490 — Drinking Water Treatment: Reverse Osmosis (peer reviewed; 2003-2008, revised September 2014)
University of Nebraska–Lincoln Extension states that only part of the water fed into a reverse osmosis system comes out as treated water, that recovery is calculated as treated water produced divided by total feed water, and that most household RO systems are designed with a 20 to 30 percent recovery rate, so a system fed 100 gallons per day at 20 percent recovery yields 20 gallons of treated water and sends 80 gallons to the waste stream. (captured 2026-09-11)
Limits: A design range for household systems, not a measurement of any particular model. NSF/ANSI 58 separately covers an efficiency rating and a recovery rating, and a listed system may be rated differently from this range.
EPA Office of Water — Home Water Treatment Facts / Filtration Facts (published November 2005)
EPA states that reverse osmosis units use approximately three times as much water as they treat, and are effective in eliminating all disease-causing organisms and most chemical contaminants. (captured 2026-09-10)
Limits: The 2005 source describes the technology class. Certification under NSF/ANSI 58 still grants claims per model, where TDS reduction is the only required one, so this does not establish what any specific unit is certified to reduce.