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Potential Revisions of Microbial and Disinfection Byproducts Rules

In January 2017, EPA announced the review results for the Agency’s third Six-Year Review (Six-Year Review 3) of NDPWRs. Based on the Agency’s review of newly available data, information, and technologies, EPA identified eight NPDWRs as candidates for revision. The eight candidates are Chlorite, Cryptosporidium, Haloacetic acids, Heterotrophic Bacteria, Giardia lambliaLegionella, Total Trihalomethanes, and Viruses. These eight NPDWRs are included in the following microbial and disinfection byproducts (MDBP) rules:

EPA is currently conducting analyses to further evaluate the eight NPDWRs for potential regulatory revisions. Additionally, with a consideration of risk/risk tradeoff among different disinfection byproducts (DBPs), EPA is also evaluating information on unregulated DBPs, including chlorate and nitrosamines.

The Agency is committed to engaging stakeholders for their input and gathering additional information to inform any potential revisions.

Public Engagement


The Safe Drinking Water Act (SDWA) requires the Environmental Protection Agency (EPA) to review each national primary drinking water regulation (NPDWR) at least once every six years and revise them, if appropriate. Revisions must maintain or strengthen public health protection.

The Six-Year Review 3 announcement was not a regulatory decision, but initiated a process involving more detailed analyses of health effects, analytical and treatment feasibility, occurrence, benefits, costs and other regulatory matters relevant to deciding whether a rulemaking to revise a regulation should be initiated.