April 15, 2026

New Water Contaminant List: What Utilities Should Know — and How to Prepare

The EPA’s latest draft of its Contaminant Candidate List does not create new regulatory obligations, but it provides an important look at where future drinking water monitoring, research and potential regulation may be headed.

The U.S. Environmental Protection Agency (EPA) released a draft of Contaminant Candidate List 6 (CCL 6) on April 2 and now is seeking public comment through June 5 on this group of unregulated substances before finalizing the list.

For drinking water utilities, the most important consideration is understanding what CCL 6 represents — and what it does not.

What is the Contaminant Candidate List?

The Contaminant Candidate List is a tool established under the Safe Drinking Water Act to identify unregulated contaminants known or anticipated to occur in public water systems and may warrant future regulatory consideration. EPA updates the list every five years and uses it to help prioritize research, occurrence data collection, and potential future rulemaking.

The draft of CCL 6 identifies 75 individual chemicals, four grouped contaminant categories — microplastics, pharmaceuticals, per- and polyfluoroalkyl substances (PFAS), and disinfection byproducts (DBPs) — and nine microbial contaminants.

The CCL does not require public water systems to monitor, treat or report any of the contaminants included. Any regulatory action would occur through a separate, formal rulemaking process.

Why Does Draft CCL 6 Matter?

While the CCL is not a regulatory mandate, draft CCL 6 offers a useful planning signal. Compared to the final CCL 5 issued in 2022, this new draft expands the number of individually listed chemicals to 75 (from 66) and increases grouped contaminant categories to four (from three previously). The list continues EPA’s class‑based emphasis on PFAS and DBPs while adding microplastics and pharmaceuticals as grouped categories.

EPA’s supporting materials suggest that microplastics remain an area with significant data gaps, while pharmaceuticals are proposed as a broadly defined group under the Federal Food, Drug, and Cosmetic Act. Together, these additions reinforce EPA’s growing focus on contaminant classes that are widespread, analytically complex, and not easily addressed through traditional regulatory frameworks.

Beyond grouped categories, draft CCL 6 highlights several individual contaminants of interest, including:

• 1,4‑dioxane
• Bisphenol A
• Lithium
• Manganese
• Methyl mercury
• MTBE

The microbial list includes organisms such as Legionella pneumophila, Escherichia coli (O157), Naegleria fowleri, Pseudomonas aeruginosa, and a pathogenic waterborne mycobacteria group — organisms that may raise treatment, distribution‑system or operational considerations even in the absence of new regulations.

What Steps Can Utilities Take Now?

Draft CCL 6 is best viewed as a planning and risk‑management signal, not a compliance trigger. Utilities may want to consider several near‑term actions:

• Assess potential blind spots. Review source‑water conditions, historical monitoring data, treatment barriers and distribution‑system vulnerabilities to understand where limited information or emerging risks may exist.
• Strengthen data to support future decisions. Targeted pre‑regulatory monitoring and improved data management can help utilities rely on defensible occurrence information rather than assumptions if regulatory discussions advance.
• Look for integration opportunities. Existing initiatives related to PFAS, DBP control, microbial risk management or advanced treatment planning may be expanded into a more coordinated emerging‑contaminant strategy.
• Engage in the comment process. Utilities and organizations with relevant data, operational experience or implementation concerns may wish to help inform the final list by giving the EPA input before the June 5 comment deadline. (EPA anticipates finalizing the list by Nov. 17.)

Draft CCL 6 does not define what EPA will regulate next, but it provides a credible view of the contaminants and contaminant classes the agency believes warrant closer attention. For utilities seeking to stay ahead of regulatory and public expectations, now is an appropriate time to organize data, evaluate vulnerabilities and begin considering future options — while the list is still in draft form.

How Freese and Nichols Can Help

Freese and Nichols works with utilities to prepare for regulatory change well before it becomes a deadline. Our teams support water and wastewater master planning, regulatory assistance, advanced treatment planning and design, distribution system water quality, DBP control, PFAS treatment, permitting, financing, construction‑phase services, and startup and commissioning. This integrated perspective helps utilities connect emerging contaminant policy discussions with practical decisions about monitoring strategies, treatment options, communications and capital planning.

Contact: James Naylor, james.naylor@freese.com or David Jackson, david.jackson@freese.com