Frequent Questions

How long can water systems increase the residual disinfectant level above the maximum residual disinfectant level (MRDL) in the distribution system to address specific microbiological contamination problems?

Water systems may increase the residual disinfectant, not withstanding for MRDLs identified in 40 CFR 141.65, including chlorine or chloramines (but not chlorine dioxide), to a level and for a time necessary to protect public health, to address specific microbiological contamination problems. Problems include, but are not limited to, distribution line breaks, storm run-off events, source water contamination events, or cross-connection events (40 CFR 141.130(d)).
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