Stormwater is in part a water quantity problem, and for decades the focus of local governments and public works officials was on how to engineer solutions to move rainwater rapidly away from urban areas to avoid the economic damages of flooding. Green infrastructure systems and practices use or mimic natural processes to infiltrate, evapotranspire, and/or harvest stormwater on or near the site where it is generated in order to reduce flows to municipal sewers. Further, the increased amount of runoff also increases pollutant loads that are harmful to aquatic life and public health into streams, rivers, and lakes. Nationally, about 750 cities operate combined sewer systems. As a result, technologies or practices called green infrastructure are receiving increased attention. The growing interest in green infrastructure practices is driven to a great extent by arguments that it is a cost-effective way to manage urban stormwater problems, particularly compared with costs of gray infrastructure. Other Non-Water Benefits. Many observers believe that the biggest barriers are lack of information on performance and cost-effectiveness, and uncertainty whether green infrastructure will contribute to achieving water quality improvements. At the federal level, there are more than two dozen funding programs in seven departments and agencies that could potentially be applicable, but there is no single source of dedicated federal funding to design and implement green infrastructure solutions. Without federal or state assistance, communities take several approaches to financing public capital projects. Local ratepayers fund most wastewater treatment needs, including stormwater projects. The number of stormwater utilities that charge fees as a dedicated funding source for projects has grown in recent years. Many municipalities try to encourage homeowners and developers to incorporate green infrastructure practices by offering incentives for both existing and planned developments. The four most common types of local incentive mechanisms are fee discounts or credits, development incentives, best management practice installation subsidies, and award and recognition programs. Some municipalities offer rebates or financing for installation of specific practices . Since 2012, the agency has awarded grants ranging from $400,000 to $950,000 to 37 communities in 23 states for projects such as developing tools and guidance to identify green infrastructure opportunities and reviewing local codes and ordinances to identify barriers to green infrastructure. EPA also has supported research evaluating green infrastructure BMPs. Congressional Interest

Congressional interest in these issues is reflected in legislation and oversight hearings in recent Congresses. Legislation titled the Innovative Stormwater Infrastructure Act of 2015 has been introduced in the 114 th Congress to support research and implementation of green/innovative stormwater infrastructure ( H.R. 1775 / S. 896 ; and Title II, Subtitle C, of H.R. 2893 / S. 1837 ). Two other bills in the 114 th Congress, S. 2768 and S. 2848 , include provisions calling for EPA to promote green infrastructure. David C. Rouse and Ignacio F. Bunster-Ossa, Green Infrastructure: A Landscape Approach , American Planning Association, Report Number 571, January 2013, 160 p.
American Rivers, Water Environment Federation, American Society of Landscape Architects, and ECONorthwest, Banking on Green: A Look at How Green Infrastructure Can Save Municipalities Money and Provide Economic Benefits Community-Wide , April 2012, 41 p.
The Nature Conservancy, Greening Vacant Lots: Planning and Implementation Strategies , December 2012, 129 p.
Christopher Kloss and Crystal Calarusse, Rooftops to Rivers, Green Strategies for Controlling Stormwater and Combined Sewer Overflows , Natural Resources Defense Council, June 2006, 54 p. 
Noah Garrison and Karen Hobbs, Rooftops to Rivers II, Green Strategies for Controlling Stormwater and Combined Sewer Overflows , Natural Resources Defense Council, 2011, 134 p.
Alisa Valderrama, Lawrence Levine, Eron Bloomgarden, Ricardo Bayon, Kelly Wachowicz, and Charlotte Kaiser, Creating Clean Water Cash Flows, Developing Private Markets for Green Stormwater Infrastructure in Philadelphia , Natural Resources Defense Council, EKO Asset Management Partners, and The Nature Conservancy, Report R:13-01-A, January 2013, 87 p.
Jeffrey Odefey, Permitting Green Infrastructure: A Guide to Improving Municipal Stormwater Permits and Protecting Water Quality , report of American Rivers, January 2013, 40 p. 
Noah Garrison, Robert C. Wilkinson, and Richard Horner, A Clear Blue Future, How Greening California Cities Can Address Water Resources and Climate Challenges in the 21 st Century , Natural Resources Defense Council, NRDC Technical Report, August 2009, 53 p.
Clean Water America Alliance, Barriers and Gateways to Green Infrastructure , September 2011, 38 p.
Center for Neighborhood Technology and American Rivers, The Value of Green Infrastructure: A Guide to Recognizing Its Economic, Environment and Social Benefits , 2010, 80 p.
Charles T. Driscoll, Caitlin G. Eger, David G. Chandler, et al, Green Infrastructure: Lessons from Science and Practice , a publication of the Science Policy Exchange, June 2015, 32 p.
Environmental Finance Center Network, Green Infrastructure Resource Directory , June 2012, 11 p.
Nell Green Nylen and Michael Kiparsky, Accelerating Cost-Effective Green Stormwater Infrastructure: Learning from Local Implementation , UC-Berkeley School of Law Center for Law, Energy & the Environment, February 2015, 51 p.
U.S. Environmental Protection Agency, Low Impact Development (LID) "Barrier Busters" Fact Sheet Series , a seven-part series of fact sheets for state and local decisionmakers, http://water.epa.gov/polwaste/green/bbfs.cfm .
For decades, stormwater, or runoff, was considered largely a problem of excess rainwater or snowmelt impacting communities. Prevailing engineering practices were to move stormwater away from cities as rapidly as possible to avoid potential damages from flooding. More recently, these practices have evolved and come to recognize stormwater as a resource that, managed properly within communities, has multiple benefits.
Stormwater problems occur because rainwater that once soaked into the ground now runs off hard surfaces like rooftops, parking lots, and streets in excessive amounts. It flows into storm drains and ultimately into lakes and streams, carrying pollutants that are harmful to aquatic life and public health. Traditional approaches to managing urban stormwater have utilized so-called "gray infrastructure," including pipes, gutters, ditches, and storm sewers. More recently, interest has grown in "green infrastructure" technologies and practices in place of or in combination with gray infrastructure. Green infrastructure systems use or mimic natural processes to infiltrate, evapotranspire, or reuse stormwater runoff on the site where it is generated. These practices keep rainwater out of the sewer system, thus preventing sewer overflows and also reducing the amount of untreated runoff discharged to surface waters.
Cities' adoption of green technologies and practices has increased, motivated by several factors. One motivation is environmental and resource benefits. Advocates, including environmental groups, landscape architects, and urban planners, have drawn attention to these practices. But an equally important motivation is cost-saving opportunities for cities that face enormous costs of stormwater infrastructure projects to meet requirements of the Clean Water Act. Other potential benefits include reduced flood damages, improved air quality, and improved urban aesthetics. However, barriers to implementing green infrastructure include lack of information on performance and cost-effectiveness and uncertainty whether the practices will contribute to achieving water quality improvements.
Another key barrier is lack of funding. At the federal level, there is no single source of dedicated federal funding to design and implement green infrastructure solutions. Without assistance, communities take several approaches to financing wastewater and stormwater projects; the most frequently used tool is issuance of municipal bonds. As a dedicated funding source for projects, the number of local stormwater utilities that charge fees has grown in recent years. Many municipalities try to encourage homeowners and developers to incorporate green infrastructure practices by offering incentives. The most common types of local incentive mechanisms are stormwater fee discounts or credits, development incentives, rebates or financing for installation of specific practices, and award and recognition programs.
The Environmental Protection Agency's (EPA's) support for green infrastructure has grown since the 1990s. The agency has provided technical assistance and information and developed policies to facilitate and encourage green infrastructure solutions and incorporate green infrastructure practices in Clean Water Act permits. EPA also has awarded grants to communities in 23 states for projects to identify green infrastructure opportunities and steps needed to overcome implementation barriers.
Congress has shown some interest in these issues. In the 114th Congress, legislation has been introduced to support research and implementation of green/innovative stormwater infrastructure (H.R. 1775/S. 896 and in provisions in H.R. 2893 and S. 1837). Two other bills, S. 2768 and S. 2848, include provisions calling for EPA to promote green infrastructure. Overall, many in Congress remain concerned about how municipalities will pay for needed investments in water infrastructure projects generally—not limited to green infrastructure—and what role the federal government can and should play in those efforts.