Accelerated chloramine decay and microbial growth by nitrification in premise plumbing

Chloramine decay rates are accelerated by nitrifier colonization of premise plumbing, which compromises the effectiveness of secondary disinfection. As expected, in the absence of nitrification, chloramine was more stable than chlorine; but in the presence of nitrification, the relative stability (and efficacy) of the two disinfectants could be reversed. The net result with chloramination can be higher levels of heterotrophic bacteria in the bulk water and pipe biofilms than would be found with free chlorine. These experimental trends were confirmed using field data collected from homes in systems with active nitrification.