A residual reading on a chart is only useful if you understand the chemistry that produced it. At the Class C level, you move from "chlorine kills pathogens" to actually running the process: knowing how much chlorine a given water demands before it will hold a residual, reading the breakpoint curve to explain why your residual sometimes behaves counterintuitively, testing correctly, diagnosing the most common field problems, and understanding why so many systems deliberately convert their residual to chloramine. This guide builds directly on the fundamentals from the Class D level.
The CT Concept, in Plain Terms
Disinfection isn't just about dose — it's about dose and time together. Regulators and operators express disinfection strength as CT: the disinfectant concentration (residual, in mg/L) multiplied by the time (in minutes) that concentration is in contact with th