Description: The Contaminant Candidate List (CCL) is a list of contaminants that, at the time of publication, are not subject to any proposed or promulgated national primary drinking water regulations, but are known or anticipated to occur in public water systems. Contaminants listed on the CCL may require future regulation under the Safe Drinking Water Act (SDWA). EPA announced the fifth Drinking Water Contaminant Candidate List (CCL 5) on November 2nd 2022. The CCL 5 includes 66 individually listed chemicals, 3 chemical groups (cyanotoxins, disinfection byproducts (DBPs), per- and polyfluoroalkyl substances (PFAS)), and 12 microbial contaminants (not displayed in the CompTox List below). The group of cyanotoxins include, but is not limited to: anatoxin-a, cylindrospermopsin, microcystins, and saxitoxin. The DBP group includes 23 unregulated DBPs that were either publicly nominated and/or among the top chemicals in the CCL 5 Universe. For the purposes of CCL 5, the PFAS group includes chemicals that contain at least one of these three structures:

    • R-(CF2)-CF(R′)R′′, where both the CF2 and CF moieties are saturated carbons, and none of the R groups can be hydrogen
    • R-CF2OCF2-R′, where both the CF2 moieties are saturated carbons, and none of the R groups can be hydrogen
    • CF3C(CF3)RR′, where all the carbons are saturated, and none of the R groups can be hydrogen

    The CompTox dashboard also includes a separate list of PFAS (WATER|EPA: Chemical Contaminants - CCL 5 PFAS subset) that meet the CCL 5 structural definition.

    The CCL Chemical Candidate Lists are versioned iteratively and this description navigates between the various versions of the lists. The list of substances displayed below represents only the chemical CCL 4 contaminants. For the versioned lists, please use the hyperlinked lists below.

    CCL5 - November 2022 This list

    CCL4 - November 2016

    CCL3 - October 2009

    CCL2 - February 2005

    CCL1 - March 1998

    Number of Chemicals: 93