CT (Disinfection) Calculator
Calculate the CT value — disinfectant concentration × contact time — for chlorine disinfection.
CT value
Formula
CT (mg·min/L) = C × T10 · T10 = baffling factor × V ÷ Q
Regulators credit only the T10 contact time (time for 10% of water to pass), not the theoretical detention time.
CT (mg·min/L) = C × T10 · T10 = baffling factor × V ÷ Q
Regulators credit only the T10 contact time (time for 10% of water to pass), not the theoretical detention time.
Baffling factor guidance
| Baffling condition | Factor |
|---|---|
| Unbaffled (mixed flow) | 0.1 |
| Poor | 0.3 |
| Average | 0.5 |
| Superior (serpentine, high L:W) | 0.7 |
| Perfect plug flow (theoretical) | 1.0 |
Note: the CT required for a given log inactivation depends on disinfectant, pathogen, temperature and pH — see the EPA CT tables (e.g. Surface Water Treatment Rules). This calculator computes your achieved CT for comparison.
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