Many utilities have switched from free chlorine to chloramine as a residual disinfectant to avoid formation of disinfection by-products in the distribution system (DS). While not generally appreciated, chloramines undergo autodecomposition, decaying to inert ionic species, thereby losing their disinfecting capacity. The decay process may be accelerated in the distribution system both in the bulk water phase and at the pipe wall. In the bulk phase, autodecomposition may be catalyzed by and chloramines may be reduced by natural organic matter as well as metallic species. At the pipe wall, chloramine decay may be accelerated by a complex set of catalyzing interactions and redox reactions with corrosion deposits, fresh metal surfaces, cement linings and biofilm. These facts suggest that chloramine is not a stable disinfectant and loss of residual within the DS can be problematic. Little is known about the rate of chloramine decay in the DS. Existing water quality models such as EPANET incorporate rate data of free chlorine decay to predict disinfectant residuals. The analogous rate data for chloramine decay rates in bulk water and at the pipe wall are needed for these models to predict chloramine residual throughout the DS. A general rate model has been derived for free chlorine decay at the pipe wall in which an intrinsic wall reaction rate may be input into DS water quality models. Research thus far on free chlorine decay has shown that the wall reaction rate is much greater than the decay rate in the bulk water. It is reasonable to expect similar behavior for chloramine decay although no quantitative assessments are available in the literature. Moreover, the wall reaction rate for chloramine may depend upon several important system characteristics: 1) pipe material because corrosion releases Fe(II) that chemically reduces chloramines, 2) water velocity because it may control mass transfer of chloramines to the pipe wall, 3) pH because many decay pathways are expected to be pH dependent and 4) temperature because reaction rates generally increase with temperature but the extent will depend on activation energies. The purpose of this research was to measure the rate of decay of chloramines in bulk water and at the pipe wall using water and pipe samples obtained from the City of Raleigh. The rate of chloramine decay in the bulk phase was measured in batch rate tests with both finished water and water obtained from various locations in the Raleigh DS. A pipe...