Detention time stops being an abstract hydraulics number the moment a regulator asks you to prove your disinfection process actually inactivates pathogens — and that proof is built entirely on the CT calculation. This guide takes everything from the earlier tiers (theoretical detention time, baffling factors, T10) and assembles it into the actual compliance math operators use under the Surface Water Treatment Rule: computing CT, checking it against a required value, and handling systems that disinfect in more than one stage.
From T10 to CT: Why Detention Time Is a Regulatory Number
Under the U.S. EPA's Surface Water Treatment Rule (SWTR) framework, public water systems using surface water — or groundwater under the direct influence of surface water (GWUDI) — must demonstrate a minimum level of pathogen inactivation through disinfection: typically expressed as required log-remova