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 This website is no longer updated and links to external websites and some internal pages may not work.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 »

Contaminant Candidate List (CCL) and Regulatory Determination

CCL 4 Frequent Questions

On this page:


What is the drinking water CCL?

The drinking water 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, and the third CCL (CCL 3) in October 2009.

What approach did EPA use to list contaminants on the CCL 4?

In selecting contaminants for the CCL 4, EPA:
  1. Carried forward CCL 3 contaminants (minus those with regulatory determinations) to the Draft CCL 4.
  2. Sought and evaluated nominations from the public for additional contaminants to consider in May 2012.  
  3. Evaluated any new available data for those contaminants with previous negative regulatory determinations from CCL 1 or CCL 2 for potential inclusion on the Draft CCL 4.
  4. Considered public and Science Advisory Board (SAB) comments and evaluated the data and information provided by commenters in selecting the Final CCL 4.

EPA published the Draft CCL 4 Federal Register notice on February 4, 2015, and requested comments on the chemical and microbial contaminants included in the Draft CCL 4. EPA consulted with SAB on the Draft CCL 4 in April 2015, and the SAB provided their recommendations to EPA in January 2016.

For more information on the process used to evaluate contaminants for the CCL 3, please see:

What contaminants are included on the Final CCL 4?

The Final CCL 4 includes 97 chemicals or chemical groups and 12 microbial contaminants that are known or anticipated to occur in public water systems. 

What changes were made from the Draft CCL 4 to the Final CCL 4?

Based on the Agency’s review of the data and information provided by public commenters, EPA is not listing three cancelled pesticides (disulfoton, fenamiphos, and molinate) on the Final CCL 4 that were listed on the Draft CCL 4. These chemicals are not known or anticipated to occur in public water systems and are not anticipated to require regulation.

With the exception of these three pesticides, all of the contaminants listed on the Draft CCL 4 are listed on the Final CCL 4.

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 Final CCL 4?

After the Final CCL 4 is published, EPA must determine whether or not to regulate at least five contaminants from the CCL 4 in a separate process called Regulatory Determination 4.  EPA will compile and evaluate additional data on the CCL 4 contaminants. The Agency will make regulatory determinations for the CCL 4 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:

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

For information on the CCL 4, please visit the EPA website, For general information on drinking water, please visit the EPA drinking water website at or contact the Safe Drinking Water Hotline at 1-800-426‑4791. Local or international calls can reach the Hotline at 703-412-3330. The Safe Drinking Water Hotline is open Monday through Friday, excluding federal holidays, from 10:00 a.m. to 4:00 p.m. Eastern time.