The Pacific Institute, a U.S.-based global water think tank, in partnership with 2NDNATURE recently released a new national assessment finding substantial opportunities for expanded stormwater capture and use approaches to improve water resilience in urban areas across the United States. 

The study quantifies the volumetric potential of stormwater runoff in urban areas, finding 59.5 million acre-feet per year (AFY) of urban stormwater runoff is generated, exceeding earlier estimates. This is equivalent to an annual average of more than 53 billion gallons per day.

The report, entitled “Untapped Potential: An Assessment of Urban Stormwater Runoff in the United States,” was developed using a spatially distributed modeling approach from 2NDNATURE to fill a gap in comprehensive national data. The analysis concludes that urban stormwater capture is currently underutilized. It also finds that greater uptake of this strategy could improve water resilience by mitigating impacts on communities from intensifying flooding and drought driven by climate change, diversifying water supplies to address water scarcity risks and reducing water pollution. While the findings are specific to the United States, insights from the assessment can inform water resilience strategies globally.

“The numbers are clear. It’s time to elevate the role of stormwater capture in the national water conversation,” says Dr. Bruk Berhanu, senior researcher at the Pacific Institute and lead author of the report. “Urban communities across the country are grappling with water scarcity risks, more severe and frequent flooding and drought due to climate change, and constraints on traditional water supplies. There is vast opportunity for stormwater capture strategies to help solve many of these challenges, enhancing overall water resilience.”

The Pacific Institute will host a webinar to discuss the report’s results and recommendations on March 19. Register here.

Key findings of the analysis include:

• National volumetric potential: Urban areas in the United States generate approximately 59.5 million AFY of stormwater on average. This is equivalent to 93% of total municipal and industrial water withdrawals in 2015, the most recent year with available data.
• Outsized coastal opportunities: Coastal sub-basins present an outsized opportunity for increased stormwater capture. While coastal sub-basins constitute just 12% of urban land area, they generate 37% (21.9 million AFY) of the national stormwater runoff potential. The authors note it is not feasible, legal or desirable to capture all urban stormwater runoff. In some areas, for example, downstream users, including ecosystems, rely on those flows to meet their water needs. However, capturing runoff in coastal sub-basins could have fewer adverse impacts on downstream users and can also improve water quality in coastal waterways.
• Top states: The states with the greatest urban area stormwater runoff potential include Texas (7.80 million AFY), Florida (4.12 million AFY), Georgia (2.77 million AFY), Louisiana (2.61 million AFY), Ohio (2.50 million AFY), Illinois (2.47 million AFY), North Carolina (2.38 million AFY), Pennsylvania (2.35 million AFY), California (2.27 million AFY) and Tennessee (2.17 million AFY). While these states show the greatest volumetric potential, the authors note there may still be a compelling case for greater adoption of stormwater capture in urban areas with lesser potential. Even in these areas, stormwater capture can make a meaningful contribution to augmenting and diversifying supplies, especially important with climate change, and can offer other benefits such as mitigating urban heat island effect and increasing community greenspace.

Stormwater capture strategies include a diverse range of approaches that can be pursued at a variety of scales. Applications include traditional grey infrastructure, such as storm sewers that route stormwater to treatment plants for reuse and storage ponds for groundwater infiltration; green infrastructure, such as raingardens and bioswales that use plants and soils to slow, filter and store stormwater in underground aquifers; and a mix of green and grey infrastructure. Green infrastructure in particular offers a range of co-benefits, including urban greening and cooling.

“This study reveals that stormwater capture presents a significant yet unrealized opportunity for enhancing urban water management across the United States,” says Dr. Nicole Beck, CEO of 2NDNATURE. “Realizing its full potential demands concerted efforts from all stakeholders involved — from researchers to policymakers and regulatory bodies, and from utilities to local communities.”

The key recommendations of the report include:

• Elevate stormwater capture on the national water planning agenda: Aligning with the U.S. Environmental Protection Agency’s Water Reuse Action Plan, the report recommends a national effort to recognize stormwater capture and use as a vital water supply strategy. It calls for the establishment of comprehensive national guidelines by federal entities to foster consistency and clarity in stormwater capture projects.
• Expand funding and financing opportunities for stormwater capture: The report points out the limited allocation of federal funds to stormwater projects and suggests enhancing accessibility to financial support for stormwater initiatives through state and federal mechanisms. Removing barriers to access of federal funds for stormwater capture can help ensure an equal playing field for alternative water strategies. Greater funding is also needed to address research gaps and support regional scale assessments that account for local context.
• Expand applications and support green infrastructure: The report encourages the treatment of stormwater for a broader range of applications, including potable and indoor uses, to maximize its integration into urban water supplies. It also recommends increased adoption of green infrastructure to support other community benefits, such as urban cooling and greenspace enhancement.
• Break down governance silos via regional approaches and interagency coordination: Emphasizing the economic challenges of individual stormwater projects and the multiple benefits of stormwater capture, the report calls for greater inter-agency collaboration and regional approaches.

The report is part of the Pacific Institute’s ongoing research advancing water efficiency and reuse strategies to build water resilience in the United States and globally. It follows the Pacific Institute’s 2022 report, “The Untapped Potential of California’s Urban Water Supply: Water Efficiency, Water Reuse, and Stormwater Capture,” which revealed California could reduce urban water use by 30% to 48% through investments in water efficiency measures, more than triple municipal water reuse and significantly increase stormwater capture across the state. The Pacific Institute plans to release additional national assessments quantifying the potential for water efficiency and reuse across the United States starting later in 2024.