Compared
Free chlorine vs. combined chlorine
Free chlorine is chlorine still available to disinfect; combined chlorine, or chloramine, is chlorine that has bonded with ammonia. Free chlorine is a stronger, faster disinfectant; combined chlorine is weaker but lasts longer in the distribution system. Total chlorine is the two added together.
Last reviewed 2026-08-04
| Free chlorine | Combined chlorine | |
|---|---|---|
| What it is | Chlorine available to disinfect | Chlorine bonded with ammonia (chloramine) |
| Disinfecting strength | Stronger, faster | Weaker, slower |
| Persistence | Fades faster | Lasts longer in the system |
| Common use | Primary disinfection | Keeping a residual across a large system |
The bottom line
They are two forms of chlorine. Free chlorine does the strong disinfecting; combined chlorine holds a longer-lasting residual. Total chlorine is the sum.
Common questions
- What is combined chlorine?
- Chlorine bonded with ammonia, also called chloramine.
- Which disinfects better?
- Free chlorine is stronger and faster.
- What is total chlorine?
- Free chlorine plus combined chlorine.