On April 6, 2026, the U.S. Environmental Protection Agency (EPA) published the draft Sixth Contaminant Candidate List (CCL 6), marking a significant step in the agency’s effort to identify and evaluate unregulated contaminants in public water systems. The CCL 6 includes 75 chemicals, four chemical groups (disinfection byproducts (DBP), microplastics, per- and polyfluoroalkyl substances (PFAS), and pharmaceuticals), and nine microbes.
This is the first time microplastics and pharmaceuticals have been designated as priority contaminant groups. While placement on the draft CCL itself does not impose any regulatory requirements, it sets the stage for future research and potential regulation of these contaminants.
About the CCL
The CCL is a list of contaminants that are not currently subject to any proposed or promulgated national primary drinking water regulations but are known or anticipated to occur in public water systems. EPA uses the CCL to identify priority contaminants for regulatory decision making and information collection. Following publication of a final CCL, EPA will determine whether to regulate any of the listed contaminants through a separate regulatory determinations process, which is governed under the Safe Drinking Water Act (SDWA).
CCL 6
The draft CCL 6 includes 88 contaminants, including the following four chemical groups:
- Microplastics: The agency wants research to understand the significant data gaps regarding microplastics’ risks in drinking water, including the need to determine the characteristics of the microplastics (e.g., colors, polymers, shapes, sizes) most associated with adverse human health effects from exposure in drinking water, the need for a validated analytical method that will allow the EPA to reliably analyze microplastics concentrations in drinking water, the need to better understand how microplastics occurring in mixtures may impact detecting specific microplastics, and the potential sources of microplastics pollution.
- Pharmaceuticals: EPA is seeking to better understand the presence and potential health effects of pharmaceuticals as a group in drinking water systems.
- PFAS: EPA has included PFAS chemicals that meet the structural definition developed for the final CCL 5 and are not currently regulated under national drinking water standards, reflecting the agency’s continued commitment to better understanding the science of this broad class of chemicals.
- DBPs: EPA is also examining disinfection byproducts, which are chemical compounds that can form when disinfectants (used in drinking water treatments) react with naturally occurring or human-made materials in water.
EPA is seeking public comment on the draft CCL 6 to determine the final CCL 6. Comments must be received on or before June 5, 2026.
EPA will also consult with its Science Advisory Board before publishing the final CCL 6. The final CCL 6 is expected to be signed by November 17, 2026.
National Context
EPA’s decision reflects a larger, nationwide effort to analyze the impacts of microplastics on human health and the environment. EPA’s action follows a similar decision in June 2025 by California’s Department of Toxic Substances Control, which proposed adding microplastics to the state’s Candidate Chemicals List for possible regulation.
In 2026 alone, Illinois, Hawaii, Vermont, Colorado, and New Jersey have introduced seven bills targeting microplastics in drinking water, state waters, wastewater, personal care products, cleaning products, and washing machines. These actions signal a growing regulatory focus on microplastics at both the federal and state levels. Stakeholders should expect this trend to continue.
Industry Takeaways
While the draft CCL 6 itself does not impose binding obligations, companies operating in the water and chemical sectors should take note of the following:
- Potential regulatory impact on public water systems and chemical manufacturers. Public water systems and chemical manufacturers may face new compliance obligations if EPA proceeds to make a positive regulatory determination for the contaminants listed on the CCL 6. Stakeholders should closely monitor EPA’s regulatory determinations process and consider engaging with the agency during the public comment period.
- Expanded sampling, reporting, and analytical requirements. EPA is also considering including microplastics in the upcoming Unregulated Contaminant Monitoring Rule (UCMR 6), which requires public water systems to monitor certain unregulated chemicals every five years (the next monitoring period is 2027 – 2031). Several parties, including seven state governors, have already petitioned EPA to include microplastics in the UCMR 6. Thus, companies should pay attention to future UCMR developments.
- Increased risk of private litigation. Heightened regulatory attention on microplastics may spur future private litigation. For example, plaintiffs’ lawyers could use EPA’s statements in the draft CCL 6 to support foreseeability and causation claims in tort and public nuisance litigation against manufacturers and water suppliers. As EPA gathers more scientific data about health impacts, the body of evidence available to litigants will grow. Companies involved in manufacturing, using, or releasing microplastics should consider evaluating their potential litigation risks.
The draft CCL 6 represents a meaningful development in drinking water regulation, particularly given the historic inclusion of microplastics. Although no immediate regulatory obligations stem from the draft CCL 6, EPA’s actions hint at an increased focus on microplastics in future rulemakings. Companies in the water and chemical manufacturing sectors should begin assessing their potential exposure and engage proactively with the regulatory process as it unfolds.
Crowell & Moring has been closely monitoring updates to microplastics rules and legislation on both the federal and state levels, and we will continue to provide updates as this area of law develops.