What’s in a List? EPA Eyes PFAS, Pharmaceuticals and Microplastics in Drinking Water

Under the Safe Drinking Water Act (SDWA), EPA is required to publish a list of contaminants meeting the following criteria: the contaminants are not subject to any proposed or promulgated primary drinking water regulations, are known or anticipated to occur in public water systems and may require regulation under the SDWA. In developing this list, EPA must consult the scientific community, consider data in EPA's national drinking water contaminant occurrence database, and may include contaminants regulated under other environmental programs, including hazardous substances identified in section 101(14) of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980, and substances registered as pesticides under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). Every five years, EPA must publish an updated list and make regulatory determinations for at least five contaminants on the list.

In April 2026, EPA published its draft Contaminant Candidate List 6 (CCL 6), the sixth iteration of the list required under the SDWA. The proposed CCL 6 includes 75 chemicals, four chemical groups (disinfection byproducts (DBPs), microplastics, per- and polyfluoroalkyl substances (PFAS), and pharmaceuticals), and nine microbes.

This article answers “what’s in a list?” through six key takeaways from EPA’s proposed CCL 6.

1. The CCL Is a “First Step” – But Not a Prerequisite or Guarantee of Regulation

   EPA describes inclusion on the CCL as the “first step” toward potential regulation under the SDWA. However, a contaminant does not necessarily have to appear on the CCL before EPA can regulate it in drinking water. The SDWA expressly recognizes that EPA can determine to regulate an unlisted contaminant, so long as the criteria for making a positive regulatory determination are met.

   The converse is also true: inclusion on the CCL does not mean EPA will ultimately determine a contaminant should be regulated in drinking water. Instead, EPA separately determines whether selected CCL contaminants warrant regulation. EPA makes a positive regulatory determination (i.e., a determination to regulate in drinking water) when it determines three statutory criteria are satisfied: (1) the contaminant may have an adverse effect on the health of persons; (2) the contaminant is known to occur or there is a substantial likelihood that the contaminant will occur in public water systems with a frequency and at levels of public health concern; and (3) regulation of the contaminant presents a meaningful opportunity for health risk reduction for persons served by public water systems. Conversely, EPA makes a negative regulatory determination (i.e., a determination not to regulate in drinking water) when it determines one or more of these criteria are not met.

   Thus, while CCL inclusion may be a “first step” toward regulation, it is neither a prerequisite to nor a guarantee of regulation under the SDWA.
    

2. A Negative Regulatory Determination Does Not Necessarily End a Contaminant’s CCL Story

   Once EPA determines a contaminant will not be regulated in drinking water and removes it from the CCL, EPA retains the authority to consider that contaminant for inclusion on a future CCL. EPA exercised this authority in developing the proposed CCL 6. In developing the proposed CCL 6, EPA reconsidered twelve (12) contaminants that had previously received negative regulatory determinations. EPA explained that this approach is consistent with the “purpose of CCL as an iterative process that aims to improve each time.” To that end, EPA evaluated whether any new health or occurrence data since the original determination indicated a positive regulatory determination could result if relisting occurred. For nine of these contaminants, EPA determined that the currently available data did not support consideration for draft CCL 6.
    

3. Microplastics Make Their CCL Debut, but EPA Says Data Gaps Remain

   For the first time, EPA has included microplastics as a group on a draft CCL. In 2022, while EPA was developing CCL 5, EPA’s Science Advisory Board encouraged the agency to consider assessing and including microplastics on future CCLs. EPA described their inclusion on draft CCL 6 as a “first step toward defining and better understanding potential public health risk from exposure via drinking water.”

   Nevertheless, EPA specifically noted because “significant data gaps” for microplastics remain, further research will be required to better understand the potential risks of microplastics in drinking water. EPA identified several of these gaps, including which characteristics of microplastics (color, size, shape, etc.) are associated with adverse health effects from exposure through drinking water; which sources contribute to the formation of microplastics in drinking water; and how microplastics interact with other substances in drinking water.

   Thus, for microplastics, CCL 6 identifies not only a potential candidate for regulation, but also the specific research questions EPA views as important to future regulatory decisions.
    

4. EPA Casts a Wide Net for Pharmaceuticals

   For the first time, EPA has proposed adding “pharmaceuticals” as a group to the CCL. However, EPA cast a wide net in defining this new group. For purposes of draft CCL 6, EPA defined the pharmaceuticals group by reference to the Federal Food, Drug, and Cosmetic Act's (FDCA) definition of a “drug,” which includes, among other things, articles intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease; non-food articles intended to affect the structure or function of the human or animal body; and articles intended for use as components of either.

   Despite the breadth of this definition, EPA's discussion of pharmaceuticals provides some indication of how the agency may prioritize individual substances for further study. In evaluating pharmaceuticals for CCL 6, EPA considered new occurrence data regarding pharmaceutical products in water and referenced that it added a data source used to identify chemicals with “estrogenic activity” (i.e., the ability to mimic or otherwise affect estrogen activity in the body).

   EPA's further evaluation of this broad group should shed more light on how this information, along with any other considerations, will shape the prioritization of specific pharmaceuticals.
    

5. PFAS and DBPs: Familiar Groups Return to CCL 6 with Some Minor Changes

   PFAS and DBPs both return as chemical groups on draft CCL 6, although their composition has changed since CCL 5: the PFAS group has narrowed, while the DBP group has expanded.

   For PFAS, EPA retained the structural definition used for CCL 5, which defines the universe of PFAS considered part of the group, while proposing to exclude any PFAS subject to national drinking water regulations at the time final CCL 6 is published (including PFOA and PFOS, for which EPA established Maximum Contaminant Levels (MCLs) in 2024).

   For DBPs, EPA added four additional unregulated DBPs (bromochloroacetonitrile, chloral hydrate, chloronitramide anion, and trichloroacetonitrile) to the group, bringing the total to 27, based on consultation with subject matter experts at the agency.
    

6. Not Every CCL 6 Contaminant Is Equally Ready for Regulatory Review

   CCL 6 does more than identify contaminants that may ultimately warrant regulation. EPA acknowledged that multiple contaminants on draft CCL 6 lack occurrence or health information needed to support a future regulatory determination, whether positive or negative. To help identify those gaps, EPA categorized chemical and microbial contaminants into four groups based on the availability of occurrence data and health assessments. EPA did not assess data availability for the PFAS and DBP groups because the availability of occurrence and health-effects data varies among the individual chemicals within each group.

   EPA described this categorization as a “starting point for identifying the data needs of the CCL 6 contaminants.” In doing so, EPA is also communicating to stakeholders where additional research may be needed to inform future regulatory decisions.

   For example, draft CCL 6 includes 75 individually listed chemicals. Although these chemicals appear on the same list, EPA's Chemical Technical Support Document indicates that they are not necessarily equally ready for regulatory review. Group A chemicals, which include 1,4-dioxane, have nationally representative finished-water data and qualifying health assessments that derive oral toxicity values. According to EPA, Group A contaminants currently have the data needed to proceed to further evaluation during the regulatory determination process, although this designation does not indicate whether EPA will ultimately make a positive or negative regulatory determination. By contrast, Group D chemicals, which include nicotine, lack a qualifying health assessment (i.e., a peer-reviewed, publicly available health assessment developed by EPA or another comparable health agency) and have various occurrence data gaps.

   So, what’s in a list? As draft CCL 6 showcases: more than a roster of contaminants that may someday be regulated. The proposed Contaminant Candidate List also provides insight into EPA’s evolving priorities, the information it believes is still needed, and where drinking water regulation may be (or not be) headed next.

   The final version of CCL 6 is expected to be signed for publication by November 17, 2026.