Stormwater presents several unique challenges when compared to its more mature water sector counterparts of drinking water and waste- water. The dispersed nature of stormwater makes responsibility for its treatment and control hard to assign. Since the promulgation of the Phase I and Phase II municipal separate storm sewer systems (MS4) regulation, communities have been faced with the task of managing stormwater flows based on early studies highlighting the potentially significant water quality effects of urban runoff.

Initial techniques to provide stormwater management focused on traditional “gray” infrastructure, but the evolution of stormwater has been heading in the direction of nature-based, or “green”, infrastructure. Similarly, the passive practices used in the first generation of stormwater infrastructure investments is starting to give way to “smart” stormwater infrastructure that uses automated controls to enhance the performance of stormwater facilities.

In addition, the view of urban runoff as being a burden has morphed into a perspective that stormwater flows are valued as significant water resources to be captured and used in strategic ways. Lastly, the rise of emerging contaminants, such as microplastics and per- and polyfluoroalkyl substances, highlights the need for true source control in stormwater programs.