Contaminant Candidate List (CCL) and Regulatory Determination

Basic Information on the CCL and Regulatory Determination

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).  SDWA requires EPA to publish the CCL every five years. SDWA directs the Agency to consider the health effects and occurrence information for unregulated contaminants as the Agency makes decisions to place contaminants on the list. SDWA further specifies that the Agency place those contaminants on the list that present the greatest public health concern related to exposure from drinking water. EPA uses the CCL to identify priority contaminants for regulatory decision making and information collection. 

Does the CCL impose any requirements on public water systems?

No. Publishing 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.

Top of Page

Why does EPA solicit public nominations for the CCL?

EPA has asked the public for information on contaminants beginning with CCL 3 to help identify unregulated contaminants that may require a national drinking water regulation and which should be considered for the CCL. The National Drinking Water Advisory Council (NDWAC) and National Academy of Sciences (NAS) recommended that EPA include public participation early in the CCL development process.

How did EPA develop CCL 1 and CCL 2?

CCL 1 was developed in 1998 based on the review by technical experts of readily available information and contained 50 chemicals and 10 microbial contaminants. In developing the CCL 1, EPA consulted with the scientific community and the National Drinking Water Advisory Council (NDWAC) on a process to identify contaminants. Based upon the NDWAC recommendations, the agency developed and used screening and evaluation criteria to develop a list of chemical contaminants for CCL 1. In 2005, CCL 2 carried forward the CCL 1 contaminants that were not removed from the list through the first regulatory determination process.

Why did EPA change the CCL process after CCL 2?

During development of the early CCLs, EPA received comments that indicated a need for a broader, more comprehensive approach for selecting contaminants for future CCLs. In response, EPA sought advice from the National Academy of Sciences – National Research Council and the National Drinking Water Advisory Council. The CCL process was revised based on their recommendations.

Top of Page

How was CCL 3 developed?

The CCL 3 development process began by compiling a broadly defined “universe” of potential drinking water contaminants. EPA then identified, assessed, and reduced the universe list to a preliminary CCL (PCCL) using simple screening criteria that indicate the contaminant’s potential for public health risk and the potential to occur in drinking water. All of the contaminants on the PCCL were then assessed based on a more detailed evaluation of occurrence and health effects along with expert judgment. The outcome of the detailed classification approach resulted in the Draft CCL 3. EPA then requested public comment on the Draft CCL 3 and published a final CCL 3 after considering the public input.

The process used to develop CCL 3 was based on the National Academy of Sciences (NAS) – National Research Council’s 2001 recommendations contained in NAS Report: Classifying Drinking Water Contaminants for Regulatory Consideration Exit and the National Drinking Water Advisory Council’s 2002 recommendations contained in NDWAC CCL report.

What happens to contaminants on the CCL?

After a final CCL is published, EPA must determine whether or not to regulate at least five contaminants from the CCL in a separate process called Regulatory Determinations. EPA will compile and evaluate additional data on all of the CCL contaminants, if available, and determine which contaminants have sufficient information to be evaluated against the three criteria listed in SDWA for making a regulatory determination.

EPA will make regulatory determinations for the five or more CCL contaminants that have sufficient data to be evaluated against the three SDWA criteria. EPA will continue to collect information, conduct and support research and/or find avenues to fill data and information gaps for contaminants that lack sufficient information to make a regulatory determination.

Top of Page

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:

It is important to note that EPA is not limited to making regulatory determinations for only those contaminants on the CCL. The agency can also decide to regulate other unregulated contaminants if information becomes available showing that a specific contaminant presents a public health risk in drinking water.

Top of Page

What criteria does EPA consider to make a regulatory determination?

When making a “determination” to regulate a contaminant in drinking water, the law requires that EPA determine whether it meets the following three criteria:

  • The contaminant may have an adverse effect on the health of persons;
  • The contaminant is known to occur or there is substantial likelihood the contaminant will occur in public water systems with a frequency and at levels of public health concern;
  • In the sole judgment of the Administrator, regulation of the contaminant presents a meaningful opportunity for health risk reductions for persons served by public water systems.

Where can I find other information on drinking water contaminants?

For general information on drinking water contaminants, please visit the EPA Ground Water and Drinking Water website or contact the Safe Drinking Water Hotline at 1-800-426-4791. The Safe Drinking Water Hotline is open Monday through Friday from 10:00 a.m. to 4:00 p.m. Eastern time, except federal holidays.

Top of Page