EPA Offers New Rule on Narrowed Definition of WOTUS

How does the agency's proposed rulemaking clarify and limit federal regulations over "waters of the United States"?

On Nov. 17, the Environmental Protection Agency and the U.S. Army Corps of Engineers (USACE) announced a proposed rule intended to clarify the definition of "waters of the United States" (WOTUS), which determines the federal jurisdiction of the Clean Water Act (CWA) for regulating pollutant discharges. This proposal follows the 2023 Supreme Court decision in Sackett v. EPA (598 U.S. 651), which significantly narrowed the definition to include only wetlands and permanent bodies of water that have a continuous surface connection to navigable waters.

Organizations can submit feedback until Jan. 5 on regulations.gov. EPA and the USACE also hosted several public meetings for those interested to share their perspectives and ask questions. The agencies are encouraging industry stakeholders to engage with them as they work toward finalizing the rule.

What's changed in EPA's new WOTUS rule?

The new proposed rule to "establish a clear, durable, common-sense definition" of WOTUS makes some key clarifications:

1. "Relatively permanent waters" are defined as standing or continuously flowing bodies of water that exist year-round or at least during the wet season. "Wet season" is intended to be locally or regionally defined.
2. Regulated wetlands must connect with a jurisdictional water body through a continuous surface connection.
3. Tributaries must have relatively permanent flow connecting them to navigable waters.
4. Ditches constructed entirely in dry land, prior converted cropland, and waste treatment systems are excluded from regulation.
5. Groundwater is explicitly excluded from regulation because it is not navigable.

New rule underscores ongoing WOTUS uncertainty

The CWA does not clearly define what constitutes WOTUS. After the CWA was enacted, EPA and USACE interpreted WOTUS broadly to include navigable waters, tributaries, interstate waters, and intrastate waters connected to interstate commerce. The 1985 Supreme Court decision in U.S. v. Riverside Bayview (474 U.S. 121) further expanded WOTUS to encompass wetlands adjacent to navigable waters. 

But in the 2006 Supreme Court case Rapanos v. U.S. (547 U.S. 715), the Court issued a plurality opinion. Justice Scalia argued for a narrower definition, covering only relatively permanent waters and wetlands with a continuous surface connection to navigable waters. In contrast, Justice Kennedy's "significant nexus" standard more broadly defined WOTUS as any water body with a significant chemical, physical, or biological connection to navigable waters. This division resulted in a patchwork of state interpretations, with some states protecting fresh water based on the "significant nexus" standard, while others adhered to the narrower definition.

What does EPA's proposed rule mean for industry?

The updated definition will impact all CWA programs that depend on the WOTUS definition, including the National Pollutant Discharge Elimination System (NPDES) permit program (section 402), the Oil Spill Prevention Preparedness and Response Program (section 311), and the Water Quality Standards and Total Maximum Daily Load Program (section 303), in addition to water quality certifications (section 401). States and tribal authorities remain free to regulate waters beyond the WOTUS definition and retain exclusive jurisdiction over groundwater.

Ultimately, any debates over the definition of WOTUS can detract from the CWA's original intent to "prevent, reduce, and eliminate pollution in the nation's water in order to 'restore and maintain the chemical, physical, and biological integrity the Nation's waters.'" But as water travels through the hydrologic cycle, it may flow in streams, rivers, wetlands, lakes, estuaries, and oceans, and it may flow between groundwater and surface water bodies as it travels. Water itself doesn't recognize regulatory definitions or state boundaries, and disturbances or pollution anywhere along its path — whether in navigable or non-navigable waters — can ultimately affect downstream water bodies. 

Any rule that regulates only some of the water bodies that are part of the hydrologic cycle can lead to ambiguity and confusion. Reducing the scope of federal regulations on waters shifts more responsibility to the states, amplifying the complexity and inconsistency of a patchwork regulatory landscape. As a result, when regulated water bodies cross state lines, state efforts to regulate those waters may lead to substantial challenges due to differing requirements and interpretations. This variability creates significant uncertainty for stakeholders across industries, who must now navigate an increasingly ambiguous and fragmented set of state-level regulations, complicating compliance and long-term planning.

Next steps for industry stakeholders

Engaging industry experts is essential for organizations involved in critical industrial applications — from data center cooling to consumer goods and electronics manufacturing — that rely on freshwater resources or discharge water to the environment. The specialized knowledge of multidisciplinary scientists and engineers can help businesses assess water sources, understand environmental impacts, maintain regulatory compliance, and advance organizational sustainability, regardless of changing definitions.

Manufacturers can still conduct thorough testing and documentation of their systems under the PMA process until a decision has been reached, as many of the processes will apply to the 510(k) process.