Introduction: Reinventing Urban Water Infrastructure

The origins of the modern discipline of environmental engineering can be traced back to the need to provide an adequate supply of safe drinking water to cities that began growing quickly during the latter part of the 19th century. Near the start of the 20th century, major investments were made in reservoirs, canals, and drinking water treatment plants. A few decades later, resources were allocated to the construction of sewage treatment plants. By the end of the 20th century, cities in the developed world had built a reliable centralized system for acquiring and delivering drinking water and collecting, treating, and disposing wastewater and urban runoff that was capable of protecting public health and the environment.

Over the past decade it has become evident that the urban water infrastructure of the 20th century may not be able to maintain the level of performance expected by society. Much of our existing water infrastructure is reaching the end of its design lifetime just as the stresses associated with climate variability and increasing populations are placing additional burdens on them. To develop new approaches to the urban water infrastructure that can meet the coming challenges, the U.S. National Science Foundation–supported Engineering Research Center for Reinventing the Nation's Urban Water Infrastructure (ReNUWIt) has embarked on a research effort on ways in which new technologies and better management practices can foster the next generation of urban water systems (www.renuwit.org). This special issue of Environmental Engineering Science highlights some of the approaches that ReNUWIt is taking to address the urban water infrastructure challenge.

The special issue begins by considering the process through which change comes to complex systems. In their overview of the innovation process, Kiparsky et al. argue that bringing a change to the urban water infrastructure requires an approach that is consistent with the institutions and the culture that surrounds urban water management. Using examples of the forces that impede and support changes in private and public enterprises, the authors provide engineers with an understanding of how the social sciences can be used to pose research questions and to identify policies that foster change.

The article on innovation systems is followed by two articles describing the ways in which active management of natural systems can enhance the performance of urban water infrastructure. In the first of these two articles, Regnery et al. describe the active management of engineered aquifer recharge systems within the urban environment, showing how advances in geophysics, hydrogeology, and microbiology can facilitate the design and operation of systems that more effectively capture and purify water during the infiltration process. This review of subsurface processes is followed by an article in which Jasper et al. show how constructed wetland systems can be built and operated in a manner that enhances the water quality. Using the engineering principle of unit processes, the authors identify an approach for making constructed wetlands a means of removing contaminants that pose risks to public health and the environment. Both articles demonstrate the potential efficiencies that can be realized if the processes affecting contaminant attenuation in natural treatment systems are considered as part of the design process.

The next three articles address ways in which urban runoff and urban rivers and streams can be managed in a manner that improves water quality, enhances groundwater recharge, and protects aquatic ecosystems. In the first article, Grebel et al. review different approaches that have been used to enhance water quality during the recharge of stormwater. They assert that these systems can achieve better water quality through inclusion of reactive geomedia and other technologies intended to remove contaminants. Bischel et al. pick up on the theme of active management of urban surface waters by describing the potential for using municipal wastewater effluent to enhance urban streams. They show that under certain circumstances, municipal wastewater effluent can serve as a valuable asset to support the aquatic habitat. They also emphasize that the concept of renewing urban streams with reclaimed water needs good case studies that include ecosystem service valuations to quantify broader societal benefits. In the third article of this group, Lawrence et al. discuss how the hyporheic zone of urban streams can be managed as natural systems and serve as a means of improving water quality and protecting the aquatic habitat. They present examples of low-flow, effluent-dominated urban streams, where there is hyporheic flow and potential pollutant attenuation.

Finally, Xu et al. review the issue of management of concentrates from water treatment processes. They describe ways in which new treatment technologies are enabling use of advanced water treatment technologies that remove salt and contaminants from water. They identify challenges associated with brine management and research needs to allow for expanded use of these systems.

Considered as a group, these seven articles provide insight into some of the major issues that must be addressed if environmental engineers are to adapt urban water infrastructure to the impending challenges that they will face in the coming decades. It is our hope that these review articles will inspire water quality researchers and practicing engineers to reconsider assumptions about the design, construction, and operation of urban water infrastructure. Additionally, we believe that the insights presented in these articles may attract the attention of public and private organizations, including regulators who make decisions about investments in the next generation of urban water systems.