Treatment process
Granular activated carbon
Highly porous carbon with an enormous internal surface area — around 1,000 square metres per gram — onto which organic molecules adsorb. It is the workhorse for taste, odour, pesticides and many micropollutants, at both municipal and household scale.
Key facts
- Scale
- Municipal and household
- Treatment stage
- Adsorption
- Certification
- Household filters are certified to NSF/ANSI 42 for aesthetic effects and NSF/ANSI 53 for health effects. The certification is contaminant-specific: a filter certified for chlorine is not thereby certified for lead.
How it works
Water passes through a bed of carbon granules. Organic molecules partition onto the pore surfaces. Capacity is finite: once saturated, the bed must be replaced or thermally reactivated, and a saturated bed removes nothing.
What it removes — and what it does not
| Row | Removes | Does not remove |
|---|---|---|
| 1 | Chlorine and chloramine, and the taste they impart | Dissolved minerals, hardness, sodium, chloride |
| 2 | Pesticides and many industrial organics | Nitrate and fluoride |
| 3 | Trihalomethanes and other disinfection by-products | Bacteria and viruses — carbon beds can in fact support bacterial growth |
| 4 | Taste and odour compounds | Most short-chain PFAS |
| 5 | Long-chain PFAS such as PFOA and PFOS, with much weaker performance on short-chain compounds | — |
| 6 | Lead, in blocks specifically certified for it | — |
Trade-offs
- Exhausts silently: performance falls with no visible change, which makes cartridge replacement discipline essential
- Can shed bacteria if left unused; household filters should be refrigerated and used promptly
- Municipal reactivation is energy intensive but avoids disposal
Related intelligence
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Sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- NSF International / American National Standards Institute — NSF/ANSI drinking water treatment unit standards. Public but restricted · Publisher terms — public access, reuse not clearly granted
- American Water Works Association — AWWA standards, water audits and utility benchmarking. Public but restricted · Publisher terms — public access, reuse not clearly granted