Corrosion Control If sequestration of iron and manganese is practiced, the chlorine residual in the water system should always be maintained at or above: By jay@americanwatercollege.org | January 11, 2017 | Certification Exams . Distribution . Water Treatment | Tags: Certification Exam Prep, Chlorine Residual, Distribution System, Iron, Manganese, Sequestration, Water Treatment