An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Drinking Water Requirements for States and Public Water Systems

Compliance Determination for Inactivation Requirements of the National Primary Drinking Water Regulations when a Public Water Systems Uses Dichlor and Trichlor for Primary Disinfection

This memorandum has been developed to assist SDWA primacy agencies (EPA Regions, states and territories) when considering inactivation/disinfection compliance requirements for those water systems that choose to use Dichloroisocyanuric acid (Dichlor) or Trichloroisocyanuric acid (Trichlor) for primary disinfection.

View other Public Water System Supervision Program Water Supply Guidance.

You may need a PDF reader to view some of the files on this page. See EPA’s About PDF page to learn more.