CCL 5 Frequent Questions

What is the drinking water CCL?

The drinking water Contaminant Candidate List (CCL) is a list of contaminants that are currently 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 uses the CCL to identify priority contaminants for regulatory decision making and information collection needs.

How often is the CCL published?

The SDWA directs EPA to publish a CCL every five years. The agency published the First CCL (CCL 1) in March 1998, the Second CCL (CCL 2) in February 2005, the Third CCL (CCL 3) in October 2009, and the Fourth CCL (CCL 4) in November 2016.

What approach did EPA use to list contaminants on the CCL 5?

In selecting contaminants for the CCL 5, EPA:

Followed the three-step process used to develop CCL 3 and CCL 4 which included building a broad universe of contaminants, screening the universe of contaminants, and classifying the contaminants to select the CCL.
Implemented improvements to the CCL process to better identify, screen, and classify potential drinking water contaminants. EPA’s approach utilized the best available data to characterize the occurrence and adverse health risks a chemical contaminant may pose from potential drinking water exposure.
Sought and evaluated nominations from the public for additional contaminants to consider in October 2018.
Evaluated any new available data for those contaminants with previous negative regulatory determinations from previous CCLs for potential inclusion on the draft CCL5.
Considered public and Science Advisory Board (SAB) recommendations and evaluated the data and information provided by commenters in selecting the final CCL 5.

EPA published the draft CCL 5 Federal Register notice on July 19, 2021 and requested comments on the chemical and microbial contaminants included in the draft CCL 5. EPA consulted with SAB on the draft CCL 5 in January 2022, and the SAB provided their recommendations to EPA in August 2022.

For more information on the process used to evaluate contaminants for the CCL 5, please see: https://www.epa.gov/ccl/contaminant-candidate-list-5-ccl-5.

What contaminants are included on the CCL 5?

The CCL 5 includes 66 chemicals, 3 chemical groups (cyanotoxins, disinfection byproducts (DBPs), and per- and polyfluoroalkyl substances (PFAS)), and 12 microbial contaminants that are known or anticipated to occur in public water systems.

What changes were made from the draft CCL 5 to the final CCL 5?

Based on the agency’s review of data and information collected during the comment period and new available data, EPA made the following changes from the draft to the final CCL 5:

EPA updated the CCL 5 Technical Support documents to include recommendations from public comment and SAB recommendations.
EPA revised the definition for PFAS to be more expansive to include additional PFAS substructures such as PFAS that are ethers or highly branched, persistence in water, and known to occur in drinking water and/or source water.

Does the CCL impose any requirements on public water systems?

No. Publication of the CCL does not impose any requirements on public water systems. If EPA decides to regulate a contaminant on the list in the future, the Agency will start a separate rulemaking process with opportunity for public comment.

What happens to contaminants on the CCL 5?

After the CCL 5 is published, EPA must determine whether or not to regulate at least five contaminants from the CCL 5 in a separate process called Regulatory Determination 5. EPA will compile and evaluate additional data on the CCL 5 contaminants. The Agency will make regulatory determinations for the CCL 5 contaminants for which there is sufficient health effects and occurrence data, and which present the greatest public health concern. EPA will continue to collect information, conduct, and support research and/or find ways to fill data and information gaps for contaminants that lack sufficient information to make a regulatory determination at that time.

What is a regulatory determination?

A regulatory determination is a formal decision on whether EPA should initiate a process to develop a national primary drinking water regulation for a specific contaminant. The law requires EPA to make regulatory determinations for at least five contaminants from the most recent CCL within five years after the completion of the previous round of regulatory determinations. To see the list of regulatory determinations for the previous CCLs, please go to: https://www.epa.gov/ccl.

Where can I find more information about this notice and the CCL?

For information on the CCL 5, please visit the EPA website, https://www.epa.gov/ccl/contaminant-candidate-list-5-ccl-5. For general information on drinking water, please visit the EPA drinking water website at https://www.epa.gov/ground-water-and-drinking-water.