Activated Carbon

carbon filtration technology chlorine pitcher block

What activated carbon is

Activated carbon is carbon (usually derived from coconut shell, coal, or wood) that has been processed at high temperature to create an enormous internal surface area. One gram of activated carbon can have a surface area exceeding 1,000 square metres — this surface area is what enables adsorption (not absorption) of contaminants passing through.

Contaminants bind to the carbon surface through physical and chemical attraction. The binding capacity is finite — once the surface area is saturated, the filter is exhausted and must be replaced.

What activated carbon removes (NSF 42 scope)

Removes effectively:

Chlorine and chloramines (the dominant use case for most UK/US city water households)
Taste and odour compounds (earthy, musty, chlorine smell)
Volatile organic compounds (VOCs): benzene, toluene, some pesticides
Sediment and particulates (carbon block, not GAC)

Does not remove effectively:

Lead — standard GAC does not; some carbon block filters do (NSF 53 scope, higher contact time required)
PFAS compounds — some advanced activated carbon media (catalytic carbon) reduce PFAS; most standard pitchers do not
Fluoride — not removed by activated carbon alone; requires activated alumina or RO
Nitrates — not removed
Bacteria and viruses — not removed; carbon can harbour bacterial growth if left saturated too long
TDS (dissolved minerals and salts) — not reduced by activated carbon

GAC vs carbon block — the practical difference

Granular activated carbon (GAC): loose granules. Used in whole-house filters, some under-sink units. Faster flow rate, lower contact time, less effective for lead and VOCs.

Carbon block: compressed activated carbon. Used in Brita, Pur, Aquasana under-sink. Slower flow rate, longer contact time, more effective for lead removal (NSF 53 achievable), eliminates channelling.

Most pitcher filters use a loose carbon media (GAC-equivalent). The contact time with slow-pour pitcher filters is longer than a faucet filter, which improves reduction rates despite using GAC.

The NSF 42 vs NSF 53 distinction

All activated carbon filters that are NSF certified hold at minimum NSF 42 (aesthetic effects). NSF 53 (health effects, including lead) requires a higher-specification carbon block formulation and independent verification of lead reduction to below 10 ppb (the EPA action level) — and from 2022, some NSF 53 certifications include PFAS scope.

Standard	Chlorine/taste	Lead	PFAS	Common products
NSF 42	Yes	No	No	Brita Standard, most GAC whole-house
NSF 53	Yes	Yes	Partial (2022+ certs)	Brita Elite, Pur Plus, ZeroWater, Aquasana AQ-5300