role of chlorine and chloramine in corrosion of lead‐bearing plumbing materials

A switch from free chlorine to chloramine disinfectant triggered problems with excessive lead in Washington, D.C., drinking water. High levels of lead originated in the service lines, but excessive lead was also derived from solder or brass plumbing materials. In many cases, the highest lead concentrations emerged from the tap after about 1 min of flushing—a troublesome outcome, given that routine public notification recommended that consumers flush for about a minute to minimize lead exposure. Bench‐scale testing found that chlorine reacts with soluble Pb +2 to rapidly precipitate a red–brown‐colored lead solid that was insoluble even at pH 1.9 for 12 weeks; this solid did not form in the presence of chloramine. Further experiments indicated that chloramines sometimes dramatically worsened lead leaching from brass relative to free chlorine, whereas new lead pipe was not strongly affected.