By Kevin Harris, Nicole Gendusa and David Boyer
On May 5, 2026, the Santa Ana Regional Water Quality Control Board (Regional Board) issued a tentative watershed-wide Municipal Separate Storm Sewer System (MS4) permit covering Orange County, Riverside County, and San Bernadino County. The permit would consolidate stormwater regulation across Santa Ana River watershed under a single regional framework. The proposal raises questions regarding whether California regulators are moving toward basin-wide stormwater permitting as a means of improving regulatory consistency, watershed management, and permit administration.
Factual Background
The federal Clean Water Act (33 U.S.C. § 1251 et seq.) requires municipalities that operate MS4s to obtain permits governing stormwater discharges. In California, these permits are typically issued by Regional Water Quality Control Boards pursuant to the federal Clean Water Act, National Pollutant Discharge Elimination System (NPDES) program, and many MS4 permits have been issued on a countywide or jurisdictional basis.
The Santa Ana River watershed spans portions of Orange, Riverside, and San Bernadino Counties. Because stormwater discharges occurring in one jurisdiction may affect downstream water quality, regulators have increasingly emphasized watershed-based planning and management strategies.
The tentative permit would establish a unified regulatory framework applicable across the watershed. According to the Regional Board, the permit seeks to improve coordination among permittees, promote consistent compliance requirements, and better address watershed-wide water quality objectives.
Regionalization of Stormwater Regulation
The watershed-wide MS4 permit reflects a broader trend toward regionalized stormwater management. Rather than regulating stormwater solely through local or county-specific permits, watershed-based permits recognize that water quality impacts frequently cross jurisdictional boundaries.
It is worth noting that the watershed-wide permit does not continue the existing permit structure by the Regional Board. Rather than renewing separate permits for Orange, Riverside, and San Bernadino counties, the Regional Board has proposed a single permit covering the entire watershed. Such decision suggests growing interest in regulating stormwater systems based more on the watershed itself than on separate local jurisdictions.
Regional permitting may provide several benefits. First, it can promote consistency in regulation among municipalities within the same watershed, which is expected to result in overall cost savings for permittees. Second, it may improve coordination of monitoring, reporting, and implementation efforts. Third, a watershed-wide approach may better align stormwater regulation of California’s river basins.
At the same time, regional permits may present challenges for permittees. Municipal agencies may face new compliance obligations, increased coordination requirements, and implementation responsibilities that differ from those imposed under prior permits. Stakeholders may also raise concerns regarding governance, cost allocation, and the extent to which local conditions are adequately addressed within a regional framework.
Another important consideration is the practical impact this permit may have on local municipalities responsible for compliance. Because the proposed permit would apply across multiple jurisdictions, cities and counties may need to coordinate more closely when implementing monitoring programs, reporting requirements, and pollution prevention efforts. Although this regional approach may improve consistency, it may also require local agencies to adjust existing compliance practices that were previously handled on an individual basis.
Conclusion and Implications
The Regional Water Control Board’s Municipal Separate Storm Sewer System permit signals a continuing shift toward basin-scale stormwater regulation in California. By regulating discharges across an entire watershed, the permit reflects a growing emphasis on integrated water quality management and regional coordination.
At minimum, the proposal shows that regulators are open to moving away from permit structures that currently govern stormwater regulation within the region. Whether similar permitting approaches begin appearing in other parts of California may help determine whether broader challenges in stormwater regulation are beginning to develop statewide.
The proposed permit also represents an effort by regulators to test whether a consolidated permit structure produces different compliance outcomes than prior regulatory approaches. Because the Santa Ana watershed operated under separate permit for decades, adoption of a single regional permit may provide regulators with an opportunity to evaluate whether basin-wide oversight leads to more effective long-term water quality management.
If adopted and successfully implemented, the permit could serve as a model for future watershed-wide stormwater permits throughout the state. Other Regional Boards may look to the Santa Ana approach when considering how to address water quality challenges that extend beyond municipal boundaries, potentially accelerating California’s movement toward basin-based stormwater regulation. The comment period ended on June 19, 2026. The Santa Ana Regional Water Quality Control Board will hold a public hearing on July 24, 2026, where it will consider adoption of the proposed permit. For more information, see:https://www.waterboards.ca.gov/santaana/water_issues/programs/stormwater/regional_ms4_permit.html
