Treatment process
Ultraviolet disinfection
Ultraviolet light at around 254 nm damages microbial DNA so that organisms cannot replicate. Its decisive advantage is that it is highly effective against Cryptosporidium, the pathogen chlorine cannot touch.
Key facts
- Scale
- Municipal and household
- Treatment stage
- Disinfection
- Certification
- Household units are certified to NSF/ANSI 55, Class A for disinfection of microbiologically unsafe water and Class B for supplementary treatment only.
How it works
Water passes a UV lamp array in a closed reactor. Dose is the product of intensity and residence time, measured in millijoules per square centimetre. Turbidity and dissolved organics absorb UV and reduce the delivered dose.
What it removes — and what it does not
| Row | Removes | Does not remove |
|---|---|---|
| 1 | Cryptosporidium and Giardia at low doses — its defining strength | Anything dissolved: chemicals, metals, nitrate, PFAS, hardness |
| 2 | Bacteria | Turbidity, which impairs it |
| 3 | Viruses, at substantially higher doses | Provides no residual protection whatsoever downstream |
Trade-offs
- No by-products and no taste or odour change
- Requires reliable power and lamp monitoring
- Must be paired with a chemical residual for distribution
- Effectiveness is invisible without dose monitoring — a failed lamp does not change the water’s appearance
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