Supreme Court Decision Clarifies Clean Water Act's Limits on NPDES Permit Requirements

On March 4, 2025, in a 5-4 decision, the U.S. Supreme Court found that the Clean Water Act (CWA) authorizes narrative (non-effluent based) criteria in National Pollutant Discharge Elimination System (NPDES) permits, but does not authorize “end-result” requirements, which put responsibility for water quality results on the discharging facility.

In City & County of San Francisco v. Environmental Protection Agency, 604 U.S. ____ (2025), the Court overturned a Ninth Circuit opinion denying San Francisco’s petition for review of an NPDES permit for a combined sewer overflow (CSO) discharge to the Pacific Ocean. San Francisco petitioned for review after two “end-result” conditions were added to the permit: one prohibiting the city from contributing to the violation of any applicable water quality standard for the receiving waters and another prohibiting the city from creating pollution, contamination, or nuisance as defined by California Water Code section 13050.

The Court rejected the Ninth Circuit’s conclusion that the plain text of the CWA and its implementing regulations provide the U.S. Environmental Protection Agency (EPA) and other NPDES permitting agencies with broad authority to impose limitations necessary to ensure the discharger’s adherence to “any applicable water quality standard.” 33 U.S.C. § 1311(b)(1)(C) (emphasis added). Instead, the Court held that Section 1311(b)(1)(C) does not authorize the EPA to include “end-result” provisions in NPDES permits — provisions that “do not spell out what a permittee must do or refrain from doing but instead make a permittee responsible for the quality of the water.” Slip Op. at 2, 20.

The Court reasoned that, “[w]hen a permit contains such requirements, a permittee that punctiliously follows every specific requirement in its permit may nevertheless face crushing penalties if the quality of the water in its receiving waters falls below the applicable standards.” Id. at 2. Rather, it is EPA’s responsibility to determine “what steps a permittee must take to ensure that water quality standards are met …, and Congress has given it the tools needed to make that determination.” Id. at 20.

Notably, the Court found that the CWA does not preclude agencies from incorporating other forms of narrative water quality standards in NPDES permits. See id. at 1-2, 9 (“[I]t is common for permits to contain ‘narrative’ provisions requiring permittees to do such things as following certain ‘best practices.’”). Based on the text of the CWA, the Court rejected a broad argument by the city that all “limitations” imposed under Section 1311 must qualify as effluent limitations rather than narrative standards. This, the Court reasoned, “would lead to either drastic consequences that the city is unwilling to embrace or a very loose interpretation of the term ‘effluent limitation’ that would undermine the city’s argument.” Id. at 8-9. Justice Barrett, joined by Justice Sotomayor, Justice Kagan, and Justice Jackson, dissented in part, joining the majority in rejecting this broad argument by the city but dissenting from the holding that EPA exceeds its authority in including “end-result” provisions in NPDES permits. Although this decision focused on a CSO permit, the Court’s ruling should effectively render all EPA and State CWA NPDES permit end-result criteria unenforceable.

Taking a step back to look at the bigger picture, this case, together with the Supreme Court’s decision in Sackett v. Environmental Protection Agency, 598 U.S. 651 (2023), speaks to this Court’s theory of environmental law. See also Sackett v. E.P.A., 566 U.S. 120 (2012). In both cases, the Court valued clarity for the regulated community, focusing on whether the person or entity being regulated could clearly understand the bright lines of what the law required in order to avoid a penalty down the road. This suggests that going forward the Court may take a dim view of novel theories of enforcement.

© Arnold & Porter Kaye Scholer LLP 2025 All Rights Reserved. This Blog post is intended to be a general summary of the law and does not constitute legal advice. You should consult with counsel to determine applicable legal requirements in a specific fact situation.