On April 2, 2026, the U.S. Environmental Protection Agency (EPA) announced a major update to its drinking water priorities with the release of the draft Sixth Contaminant Candidate List (CCL 6) for public comment. For the first time since the Contaminant Candidate List program began, EPA designated microplastics and pharmaceuticals as priority contaminant groups for drinking water evaluation. Previously, CCLs focused on individual contaminants.
What is the EPA Contaminant Candidate List (CCL)?
The CCL is a regulatory tool required under the Safe Drinking Water Act (SDWA). Every five years, EPA publishes a list of contaminants that are not yet subject to national primary drinking water regulations, but are known or anticipated to occur in public water systems and may warrant future regulation. The CCL does not establish enforceable standards on its own. Rather, it serves as the first step in a longer regulatory pipeline, prioritizing contaminants for research, data collection, monitoring, and eventual regulatory determination.
To develop the draft CCL 6, EPA applied its established three-step screening framework used in prior CCL cycles.
- Step 1: EPA identified a broad universe of potential drinking water contaminants, called the CCL 6 Chemical and Microbial Universes, which included approximately 25,000 chemicals and 1,450 microbial contaminants.
- Step 2: EPA applied screening criteria to the CCL 6 Chemical and Microbial Universes. Based on their potential to occur in public water systems and their potential for public health concern, EPA identified 240 chemicals and 36 microbial contaminants, called Preliminary CCLs (PCCLs), for further evaluation.
- Step 3: EPA selected chemical and microbial contaminants from each respective PCCL to include on the draft CCL 6 based on more detailed evaluation of occurrence, health effects, and expert judgment.
The draft CCL 6 includes 75 individual chemicals, nine microbes, and four contaminant groups: microplastics, pharmaceuticals, per- and polyfluoroalkyl substances (PFAS), and disinfection byproducts (DBPs). Notably, few individual PFAS have already gone through previous CCLs and are currently regulated under the Safe Drinking Water Act (SDWA). Other compliance programs such as the Toxic Substances Control Act (TSCA) have implemented regulations encompassing PFAS defined as groups. Though, the latter define the scope of the TSCA rule (i.e., which PFAS fall under the rule) rather than serve as the regulatory objects by themselves.
Why Microplastics and Pharmaceuticals Matter as Priority Contaminant Groups
The inclusion of microplastics and pharmaceuticals as groups, rather than individual substances, marks a significant shift in how EPA is approaching complex and variable mixtures of emerging contaminants.
Microplastics in Drinking Water
Microplastics are small plastic particles that persist in the environment and have been detected in surface water, groundwater, treated drinking water sources, and even foodstuff. By adding microplastics to the CCL as a priority group, EPA is signaling the need for:
- Improved detection and analytical methods
- Better understanding of occurrence in drinking water systems, i.e., monitoring
- Additional study of potential human health impacts
Pharmaceuticals in Drinking Water
Pharmaceuticals can enter water systems through human excretion, wastewater discharges, and improper disposal. The draft CCL 6 identifies pharmaceuticals as a priority contaminant group due to their widespread use, environmental persistence, and biological activity. Alongside the draft CCL, EPA released human health benchmarks for 374 pharmaceuticals. These benchmarks are:
- Non‑regulatory and non‑enforceable
- Intended as screening tools to help states, Tribes, and local water systems evaluate potential risk when pharmaceutical residues are detected
The benchmarks do not establish drinking water standards but provide context for interpreting monitoring or investigative data.
CCL 6 Public Comment and Timeline
The draft CCL 6 will be published in the Federal Register, opening a 60-day public comment period. EPA will also consult with its independent Science Advisory Board before finalizing the list. The final CCL 6 is expected to be signed by November 17, 2026.
As with previous contaminant candidate lists, additional years of data collection and evaluation are required before any regulatory determinations are made.
How does CCL 6 Impact Current Public Water and Drinking Water Systems?
EPA’s announcement does not create new drinking water regulations, require immediate monitoring or treatment changes, or establish enforceable limits for microplastics or pharmaceuticals. Additionally, no new monitoring requirements, treatment standards, or reporting obligations take effect as a result of this announcement.
The CCL is a priority-setting tool, not a regulation. However, the CCL 6 signals the direction EPA intends to move. Environmental professionals and water system operators should watch for regulatory determinations that will follow the finalized list, track developments in analytical methods for emerging contaminants, and consider how the pharmaceutical benchmarks may shape local decision-making in the near term.
Over time, information gathered through the CCL process can influence future regulatory decisions and monitoring programs. Past CCLs resulted in adding certain contaminants to the Unregulated Contaminant Monitoring Rule (UCMR) requiring public water system monitoring. We keep an eye out for this development.
