Compared
Chlorine vs. UV disinfection
Chlorine and ultraviolet light are two ways to disinfect water. Chlorine adds a chemical that leaves a lasting residual to keep protecting the water; UV light inactivates organisms as water passes a lamp but leaves no residual. Drinking water systems need a residual, so chlorine is standard; UV is common in wastewater.
Last reviewed 2026-08-04
| Chlorine | UV light | |
|---|---|---|
| How it works | A chemical dose | Ultraviolet light on passing water |
| Leaves a residual | Yes | No |
| Byproducts | Can form disinfection byproducts | None from the light itself |
| Common in drinking water | Yes, a residual is required | Only with a residual added |
| Common in wastewater | Yes, often dechlorinated after | Yes |
The bottom line
Because distributed drinking water must carry a disinfectant residual, chlorine is the standard there. UV shines where a residual is not required, like much of wastewater.
Common questions
- Why does drinking water use chlorine?
- It leaves a residual that keeps protecting the water through distribution.
- Does UV leave a residual?
- No, which is why drinking water systems still need a residual.
- Which makes byproducts?
- Chlorine can form disinfection byproducts; UV light does not.