This cost-benefit analysis evaluates stormwater management options in Chicago by comparing the welfare effects of the McCook Reservoir expansion to green roofs and rain barrels, two leading forms of green stormwater management promoted by the EPA. Based on our findings, expanding green roof programs to encourage broader residential implementation—ultimately, doubling the city’s existing green roof space—would improve stormwater management, limit combined sewage overflows (CSOs), and better prepare Chicago for increased rainfall.